the characters of which are of systematic importance. The first region is the colon, which forms a very simple expansion in mammals such as Carnivora (fig. 5), where the whole hind-gut is relatively short, or a series of simple loops in mammals in which the whole gut has a primitive disposition (e.g. Marsupialia, fig. 6). In the odd-toed Ungulata, the colon (fig. 7) forms an enormously long loop, the two limbs of which are closely approximated and the calibre of which is very large. 
Fig. 9.—Intestinal Tract of Gorilla. S, cut end of duodenum; R, cut end of rectum; C, vermiform appendix of caecum; X, X2, X3, cut ends of factors of the portal vein.In Ruminantia (fig. 8) the colon is still more highly differentiated, displaying first a simple wide loop, then a complicated watchspring-like coil, and finally a very long, irregular portion. In the higher Primates (fig. 9) it forms one enormous very wide loop, corresponding to the ascending, transverse and descending colons of human anatomy, and a shorter distal loop, the omega loop of human anatomy. Other striking patterns are displayed in other mammalian groups.
The second region of the hind-gut is usually known as the rectum, and although it is sometimes lengthened it is typically little longer than the portion of the primitive straight gut that it represents.
Adaptations of the Intestinal Tract to Function.—The chief business of the gut is to provide a vascular surface to which the prepared food is applied so that the nutritive material may be absorbed into the system. Overlying and sometimes obscuring the morphological patterns of the gut, are many modifications correlated with the nature of the food and producing homoplastic resemblances independent of genetic affinity. Thus in birds and mammals alike there is a direct association of herbivorous habit with great relative length of gut. The explanation of this, no doubt, is simply that the vegetable matter which such creatures devour is in a form which requires not only prolonged digestive action, but, from the intimate admixture of indigestible material, a very large absorbing surface. In piscivorous birds and mammals, the gut is very long, with a thick wall and a relatively small calibre, whilst there is a general tendency for the regions of the gut to be slightly or not at all defined. Fish, as it is eaten by wild animals, contains a large bulk of indigestible matter, and so requires an extended absorbing surface; the thick wall and relatively small calibre are protections against wounding by fish bones. In frugivorous birds the gut is strikingly short, wide and simple, whilst a similar change has not taken place in frugivorous mammals. Carnivorous birds and mammals have a relatively short gut. In birds, generally, the relation of the length and calibre of the gut to the size of the whole creature is striking. If two birds of similar habit and of the same group be compared, it will be found that the gut of the larger bird is relatively longer rather than relatively wider. The same general rule applies to Meckel’s tract in mammals, whereas in the case of the hind-gut increase of capacity is given by increase of calibre rather than by increased length.
The Colic Caeca.—These organs lie at the junction of the hind-gut with Meckel’s tract and are homologous in birds and mammals although it happens that their apparent position differs in the majority of cases in the two groups. In most birds, the hind-gut is relatively very short, and the caecal position, accordingly, is at a very short distance from the posterior end of the body, whereas in most mammals the hind-gut is very long and the position of the caecum or caeca is relatively very much farther from the anus. Next, in most birds, the caeca when present are paired, whereas in most mammals there is only a single caecum. On the other hand, in certain birds (herons) as a normal occurrence, and in many birds as an individual variation, only a single caecum occurs. In some mammals, e.g. many armadillos, in Hyrax and the manatee, the caeca are normally paired; in many other (e.g. some rodents and marsupials) in addition to the normal caecum there is a reduced second caecum, whilst in quite a number of forms the relation of the caecum, ileum and colon at their junction is readily intelligible on the assumption that the caeca were originally paired. The origin and many of the peculiarities of the ileo-caecal valve find their best explanation on this hypothesis.
The caeca are hollow outgrowths of the wall of the gut, the blind ends being directed forwards. The caecal wall is in most cases highly glandular and contains masses of lymphoid tissue. In birds and in mammals this tissue may be so greatly increased as to transform the caecum into a solid or nearly solid sac, the calibre of which is for the most part smaller than that of the unmodified caecum. In some birds, the whole area of the caecum may be modified in this way; in mammals, it is generally the terminal portion, which then becomes the vermiform appendix, familiar in the anthropoid apes, in man and in some rodents. It is difficult to see in this modification merely a degeneration; not improbably it is the formation of a new glandular organ.
The caeca exhibit almost every gradation of development, from relatively enormous size to complete absence, and there is no definite, invariable connexion between the nature of the food and the degree of their development. In the case of birds, it may be said that on the whole the caeca are generally large in herbivorous forms and generally small in insectivorous, frugivorous, carnivorous and piscivorous forms, but there are many exceptions. Thus, owls and falcons have a diet that is closely similar, and yet owls have a pair of very long caeca, whilst in the Falconidae these organs are much reduced and apparently functionless. The insectivorous and omnivorous rollers,motmots and bee-eaters have a pair of large caeca, whilst in passerine birds of similar habit the caeca are vestigial glandular nipples. It is impossible to doubt that family history dominates in this matter. Certain families tend to retain the caeca, others to lose them, and direct adaptation to diet appears only to accelerate or retard these inherited tendencies. So also in mammals, no more than a general relation between diet and caecal development can be shown to exist, although the large size of the single caecum of mammals is more closely associated with a herbivorous as opposed to a carnivorous, frugivorous, piscivorous or omnivorous diet than is the case in birds. There is no relationship between diet and the complete or partial presence of both members of the primi-pair of caeca in mammals, the occurrence of the pair being rather an “accident” of inheritance than in any direct relation to function.
Literature.—T. W. Bridge, in The Cambridge Natural History (vol. vii).; D. S. Jordan, A Guide to the Study of Fishes; R. Owen, Anatomy of Vertebrates; M. Weber, Die Säugethiere; W. H. Flower, The Organs of Digestion in Mammalia; R. Wiedersheim, Lehrbuch der vergleichenden Anatomie der Wirbelthiere; A. Oppel, Lehrbuch der vergleichenden mikroskopischen Anatomie der Wirbelthiere; Chalmers Mitchell, “The Intestinal Tract of Birds,” Transactions of the Linn. Soc. of London (vol. viii., 1901); and “On the Intestinal Tract of Mammals,” Transactions of the Zool. Soc. of London (vol. xvii., 1905). (In the two latter memoirs a fuller list of literature is given.) (P. C. M.)
ALIMONY (from Lat. alere, to nourish), in law the allowance for maintenance to which a wife is entitled out of her husband’s estate for her support on a decree for judicial separation or for the dissolution of the marriage. Though, as a rule, payable to a wife, it may, if the circumstances of the case warrant it, be payable by the wife to the husband. Alimony is of two kinds, (a) temporary (pendente lite), and (b) permanent. Temporary alimony, or alimony pending suit, is the provision made by the husband for the wife in causes between them to enable her to live during the progress of the suit, and is allowed whether the suit is by or against the husband and whatever the nature of the suit may be. The usual English practice is to allot as temporary
