1890.] A. Alcock — On the Gestation of Elasmobranch Fishes. 55 



tissue in longitudinal bundles, the united thickness of the two layers 

 being about one-nineteenth of an inch ; (4) a mucous layer of varying 

 thickness, containing numerous blood-vessels and lymphatic (?) spaces, 

 and crowded with lymphoid cells. 



This mucous layer forms the long papillae above mentioned, and a 

 uniform sheet of close-set tubular glands, which resemble, for the most 

 part, the lieberkuhnian follicles of human anatomy, covers its entire sur- 

 face, both papillary and inter-papillaiy. These glands, at any rate near 

 their orifices, are lined with short columnar epithelial cells, and similar 

 cells invest the surface of the mucous membrane between the orifices 

 of the glands. 



The individual papilla?, as already stated, are about half an inch 

 long, and are flattened. In some cases they bifurcate or trifurcate. 

 In breadth they vary from one forty-eighth to one twenty-fourth of an 

 inch. They are formed by a central prolongation of the mucous coat 

 richly provided with lymphoid cells, and containing at least one blood- 

 vessel and numerous lymphatic (?) spaces ; and are invested externally 

 by the above-described layer of tubular glands. These glands are 

 mostly simple at the bases of the papilla?, but peripherally they fre- 

 quently become racemose, and in this case the acini are lined internally 

 with a cubical epithelium. 



As to the function of this vast surface of glandular tissue, we are 

 able to form an opinion by referring to the case of Trygon bleeheri. 

 There we found a uterus exactly similar in its naked eye anatomy to 

 the one we are discussing ; and in this uterus was a large foetus entirely 

 separate, as far as structural connexion goes, from the mother ; while 

 the uterine papillaiy Surface was concealed by a copious secretion of 

 a highly albuminous, and presumably nutritive, fluid. In the absence of 

 any vascular connexion between the foetus and the mother, we assumed 

 that this fluid served for the nutrition of the foetus. 



In Myliobatis nieuhofii, in which the uterine papilla? are less 

 attenuated, and more amenable to manipulation, we find the whole 

 intra-uterine mucous membrane forming a superficial gland ; and I 

 think we are justified in assuming that this gland is practically a milk- 

 gland, the secretion of which furnishes the developing fcetus with nutri- 

 ment. 



In the Zoological Record the only allusion to uterine villi that I can 

 find is to a paper by Trois, in the " Atti del Institute Veneto " Vol. II, 

 p. 429, " On the uterine villi of Myliobatis noctula and Gentrina salvi- 

 ani :" but I regret that I have not been able to obtain access to this. 



