64 J. T. CUNNINGHAM. 



vitelline membrane. In the figure a wide interval is shown 

 between the vitelline membrane with its processes and the 

 epithelium with its pits, but as in the former case, there can be 

 no doubt that this is merely a result of the process of prepara- 

 tion ; in the natural condition the membrane was in .contact 

 with the epithelium, and its processes filled up completely 

 the pits in the latter. It is rather curious that the epithelium 

 thins out very much over the tops of the processes, and this 

 would seem to be in opposition to the belief that the vitelline 

 membrane, processes and all, is due to the secretory activity of 

 the epithelium ; but it is probable that the formation of the 

 processes takes place at the sides where the epithelium is very 

 thick, and that they are pushed up by growth at the base. In 

 these processes, rudimentary as they are, it is not difficult to 

 recognise the early stages of the polar threads which distin- 

 guish the ripe deposited egg of Myxine. Here, then, at last 

 we have the explanation of these processes, which have hitherto 

 received no interpretation except the erroneous one of Allen 

 Thomson. The capsule enclosing the ripe ovum is undoubtedly 

 the vitelline membrane, and the polar threads are processes 

 from this. I have already pointed out that I have ascertained 

 by actual examination that these processes are not tubular, as 

 Allen Thomson supposed, but solid. Thus, there is no homo- 

 logy or comparison possible between the capsule of the egg of 

 Myxine with its polar threads, and the horny capsule in which 

 the eggs of oviparous Elasmobranchs are enclosed. The 

 Elasmobranch capsule is produced by a special gland in the 

 oviduct, and the fact that Myxine has no oviduct might alone 

 have prevented the comparison which was instituted by Dr. 

 Thomson, and which so many authors have repeated. Refer- 

 ring, again, to fig. 4, it is seen that the vitelline membrane 

 has much increased in thickness since the stage shown in 

 fig. 2. The proliferation and differentiation of cells at the pole 

 in the follicular epithelium has disappeared, but the cylinder 

 of cells, though reduced in size, still remains in the micropyle, 

 and is evidently destined to keep the latter open until the 

 maturation of the ovum is complete. Close beneath the 



