small worm was a different species, we ought to see in it eggs in course of development, which, however, I have never found to be the case.
The extraordinary disproportion in size between the sexes, though an extreme case, is not entirely without analogy in the animal kingdom. Nordmann first ("Micrographische Beitrage," Pt. 2—see also Huxley's Lectures, "Medical Times and Gazette," August 22nd, 1857, p. 187), discovered that in certain Crustacea the males are much smaller than the females. This is the case, principally, in the genera Actheres, Brachiella, Chondracanthus, and Anchorella, in which the minute male may generally be found attached to the female in the neighbourhood of the vulva. The minute and "complemental" males, discovered by Mr. Darwin in the genera Scalpellum and Ibla, afford cases in point from among the Cirripedia.
In spite, however, of analogies pointing in the same direction, one cannot but be astounded at the existence of a species in which, as in the present, the male is more than twenty-eight thousand times smaller than the female, which, if we may so say, belongs to, it.
I was not able very satisfactorily to ascertain the manner in which the two are fastened together; but it seemed as if the large worm had a small sac-like depression of the skin, Pl. 1, f. 14, into which a corresponding projection of the small one closely fitted. The inner contents of the body passed into the projection, but I could not perceive any penis or spermatozoa, nor was the ovary of the female connected with the place of attachment. The two creatures adhere together more closely than this condition, taken by itself, could account for; and, as in the somewhat similar case of Syngamus the union is effected by the presence of a sort of cement, it was natural to suppose that the same might be the case here. Neither Mr. Busk, however, who was kind enough to look at the junction, nor I, could see any trace of cement; and it is evident, therefore, that if the two skins are not continuous, they are, at least, perhaps by long contact, very closely united to one another.
Considering all these facts, there seems every probability that in this little creature we have the male Sphærularia; but until the Spermatozoa and the transformations are known to us, the fact cannot be regarded as being conclusively established.
It only remains for us to consider the natural position and affinities of Sphærularia, though it will not be possible to come to any satisfactory conclusion until we know more of the anatomy and development of the young. It is, of course, evident that Leon Dufour was right in placing it among the Nematodes; but when that order was limited by the separation of the Gordiacei, it is not so clear that it is correct to leave Sphærularia in its former position. The principal differences between the two orders (Siebold, "Anat. comp.," t. i., p. 113), as given by Siebold, are that the true Nematodes possess an anus and an organ for copulation, while in Gordiacei the one is always, and the other sometimes, wanting. According to both these characters, Sphærularia would belong to the latter order, in which, accordingly, it is correctly classed by Diesing and Meissner, although V. Siebold, Rudolphi, Owen, and other
