Natural History Review/Series 2/Volume 1/Number 4/On Correlations of Growth, with a Special Example from the Anatomy of a Porpoise
Philosophers of other countries have often taken occasion to remark, and in no complimentary terms, upon the utilitarian tendency constantly displayed by the English mind. Our everlasting seeking after hidden purposes, our infantine inquisitiveness after final causes in biological as well as other investigations, has frequently called forth contemptuous comments from foreigners, who happened to be acquainted with Bacon's famous comparison of final causes to vestal virgins. But in these latter days it has come to be acknowledged, even in England, that there are many structures in normal organisms for the existence of which no teleological explanation will suffice; and it is right to say that in no other country, and in no other time than ours, have theories for the explanation of such phenomena been more clearly enunciated. Our natural hankering after hypothesis, our constitutional craving after rationales, has called into use, if not into being, the several theories of adherence to type, of complemental nutrition, of genealogical, yet modified, transmission, and of correlation of growth.
The first of these theories has won with us not a little popularity; its antique dress, striking the eye, diverted the attention from tie utter incongruity which exists between Platonic mysticism and modern science; and, appealing to our reverence for the dreams of our youth, it has lived longer, and made more converts than unassisted by the associations of the Academy it ever could have done. Even now it is fairly in the way of developing out of the larva stage of an Idolon Theatri into an Idolon Fori, a more active, elusive, albeit fragile, Imago. But a few years back, the joint empire of final and formal causes, of confederated ideological and morphological considerations, seemed firmly established in a country delighting in compromise; the legitimacy of the one, and the prescriptive right of the other, placed them, when united, in an apparently unassailable position. The appearance of the theory of complemental nutrition in a deservedly well-known work[1] caused men to accept of a triumvirate of ruling causes. Material causes counted for something as well as final and formal; Wolff's theory could suffice not only for the rationalization of many phenomena which Paley and Oken did explain, but also for the elucidation of some with which their philosophies were incompetent to deal. Mr. Paget's exemplifications of the law of complemental nutrition seem drawn exclusively from a class of cases of what I would call "heterogeneous growth." The evolution of the one structure has rendered possible the evolution of the other, by setting free some residual product which Nature in her economy has worked up into such secondary structure. The perfecting of the plumage contemporaneously with the perfecting of the sexual functions in the pairing bird is one, and may serve as a type of all, of the instances given by Mr. Paget. There is no equality in rank between the two structures, which stand to each other in this relation of complemental nutrition; the one is supported by what the other finds useless, superfluous, or even hurtful; after the production of the one the organism aims and labours, the other is but a "nebenprodukt;" they are heterogeneous in the same sense as the food of the hound and the food of his master, and often in a yet truer sense still.
The instances of Correlated Growths to which I am about to refer, and which from the dissection I shall detail, I hope to elucidate, differ from those classed under the head of Complemental Nutrition, in that both growths draw with equal right, and to an equal extent, upon the same store of nutriment. To the same stock of alimentary matters they stand in the same relation; they share and share alike either as joint consumers or joint elaborators of it. If we may coin a word from but second-hand Greek, and borrow one-half of our composite from our Anglicised word "tautologous," we would call these growths "tautogeneous." As just hinted, they admit of a two-fold rationale. The blood either needs, as in the case I shall proceed to detail, an excess of some material, or it possesses some material in excess over its requirements; in either case "tautogeneous" growths spring up, in the one case to elaborate, in the other to consume, that excess of material. The history of pathological tumours is but an illustration of the latter of these divisions. The severity of our struggle for existence has called into being so rigid a law of parsimony, as to render it difficult to give illustrations of this class of tautogeneous growths from physiological nutrition. But though difficult, it is not impossible. I proceed to illustrate the former of these two divisions by an account of certain structures observed by me in a recent dissection of a young porpoise.
The animal was a young Phocæna communis, but it had attained at least fourth-fifths of its full size, weighing as it did 60 lbs. and being 4714 inches in length.
On either side the aorta, just where it became free from the diaphragm, on passing into the abdomen, two elongated bodies were to be seen, lying in close contact with the posterior part of its calibre for a length of as much as three inches. Their width was about the fourth of an inch, and this width was maintained for their entire length. Their external surface was smooth, only a little lobulated at their upper end and internal margin. They possessed a readily detachable fibro-cellular capsule. They were reddish in colour, firm to the touch, on section at first homogeneous, but subsequently showing to careful inspection numerous orifices of cut vessels, though very little fibrous stroma. Their upper ends lay behind, and in contact with the posterior half of each supra-renal capsule. This relation will show that the structures in question could not have been abnormally persistent Wolffian bodies, which indeed further particulars will yet further prove.
These structures, when examined by the microscope, were seen to be all but wholly made up of such cells as we get from the Malpighian bodies in the spleen, or indeed from the cortical part of a lymphatic gland, namely, circular nucleated cells with granular contents, of a size somewhat less than that of a red blood corpuscle.
Functionally, these structures may be regarded as identical with lymphatic glands; morphologically, I consider them different; on account, first, of their symmetrically elongated tongue-like shape, all but entirely smooth and unlobulated, and secondly, on account of their encapsulation in an external coat of fibro-cellular tissue, and their want of such supporting elements within their parenchyma.[2]
There can at all events be no doubt that they were developed from the genera] formative mass of blastema, which surrounds the aorta in the fetus, as described by Professor Goodsir;[3] and that therefore they were morphologically as well as physiologically to be classed with the thymus.[4] This gland, as well as the thyroid, was largely developed in this specimen, and the arrangement Of the two glands coincided very exactly with the description given of them by my friend Mr. Turner.[5]
The lymphatic glands generally throughout the body were largely developed; so largely, in fact, at either jaw angle, as to simulate the appearance of a large submaxillary gland.
The spleen was, as has been so often described, curiously multifid.
All of these ductless, all of these lymphatic, glands were richly supplied with blood vessels; all, alike and jointly, laboured at the elaboration of the constituent elements of the vast mass of this cetacean's blood. They enabled it thus to support a high standard of temperature in an excellent conducting medium, and they supplied all the calls for rich and refined aliment which a brain equalling in this case one-sixtieth of the weight of the entire body, made upon the nutritive fluids. They may be taken as illustrations of "tautogeneous growths" of the first of our two classes.
Many of Mr. Paget's instances of complemental nutrition, Mr. Darwin would explain as the results[6] of hereditary transmission, with modification, and there can be little doubt that of the two hypotheses the latter will, to many minds, seem to suit the better with such instances as the four rudiments of nails on the fun of the Manatee, or the equally rudimentary teeth in the Ruminant's intermaxillaries, or of the representatives of the Polian vesicles in the Arenicola.
But many of Mr. Paget's instances cannot be brought under this head, and constituted as our minds are, we cannot but read them as he has done.
Mr. Darwin, on the other hand, himself[7] admits that there are many instances of correlated growths of which our reason can give no rationale, either as subserving ends, or as confirming to type, or as speaking of parentage, or as working up into structure what would else be waste and excretory; for which in other words it can assign neither final nor formal, nor material cause. I would instance in addition to those he brings forward, the correlations of growth witnessed in Morbus Cæruleus betwixt a malformation of the heart and a clubbed adunque state of the finger nails, and in Morbus Addisoni betwixt disorganized supra-renal capsules and pigmentary skin discolouration. Unable to rationalize, we class such phenomena as these under the wide head of "Correlations of Growth." The very vagueness of the phrase prevents us from even momentarily deluding ourselves with the idea that it amounts to an explanation, and to more therefore than an expression, of facts. It cannot be accused of striving to conceal the flimsiness of its thought by a magnificent display of archaic words, as certain exchequers would fain conceal their bankruptcy from the world by a copious issue of paper money. Herein lies its great merit.
On a future occasion I shall consider the nature of the Hybernating glands, if so they may be called, of certain hybernating and non-hybernating Insectivora and Chiroptera, and the possibility of classing them as growths tautogeneous with the highly developed mesenteric and cervical lymphatic glands found in many of those creatures.
And, before concluding, I would mention yet another class of structures, the existence of which admits of being rationalized upon yet another principle. These structures, fixed and settled in the adult organism, speak of a time when the sex was as yet unfixed and unsettled in the developing embryo, and accessory organs of either kind were, if so we may say, prepared so as to be in readiness to meet either event. The mammary glands, the Weberian organ, and the cysts of Morgagni of the adult male, the round ligament and the canals of Nuck and of Gärtner of the adult female economy, may have the history of their existence thus read.
As more and more vera causæ assert their existence and vindicate their rights, the ancient realm of Archetypal Ideas will suffer more and more serious curtailment.[8] But, like other foiling empires, it too will find its advocates to speak of it as being an "essentially conservative power;" though after short campaigns it has, once and again had to resign some of the fairest provinces in the world of thought, its existence will still be said to be necessary for the "preservation of the due balance of power" amongst rival biological principles.
Let us hope that in the interludes of Rhetoric the Logic of Facts may find a moment to make itself heard. It will teach men mundum quærere non in microcosmo suo sed in mundo majore, to hold of Nature that her ways are not as our ways, nor her thoughts as our thoughts. The notion of type may help man's weakness, but it by no means therefore follows that it regulates Nature's operations; it may enable us to colligate phenomena, but it may no more for that be the cause of their evolution than the mule's panniers which carry home the grapes are, by virtue of this their function, the cause of the growth of the vine.
- ↑ Paget Lectures on Surgical Pathology, Vol. 1, Lecture ii.
- ↑ Though my dissection enables me to confirm the views put forth by Mr. Turner, it compels me to dissent from those anatomists who say there is nothing in the Cetacean economy to represent either the Vena Azygos or the Cowper's Glands of Human Anatomy.
- ↑ Phil. Trans. 1846, p. 638.
- ↑ In the common Shrew, however, two bodies are to found, floating loosely in the abdominal cavity, but anchored each by a process of mesentery which is attached just where these bodies in the Porpoise lie fixed; and that they are connected with the lymphatic or rather with the lacteal system, an examination of a Shrew, which has died whilst digesting, will leave no doubt.
- ↑ Transact. Royal Soc. Edinburgh, Vol. XXII. Part ii.
- ↑ Origin of Species, p. 453-454, 1st edit. pp. 486-487, 3rd edit.
- ↑ Origin of Species, pp. 145, 197, 1st edit.; pp. 162, 217, 3rd edit.
- ↑ Even in Mr. Herbert Spencer's "First Principles," we find at page 22, the following sentence. "In Biology we are beginning to progress through a fusion of the Doctrine of Types with the doctrine of adaptations," and Mr. Darwin, in the last page but one to which we have referred in his writings, speaks of "Homology coming into play" as a really efficient physical agent.