340 
provided. From this time, until all the yolk is absorbed, the gut is 
found to contain it. 
It became of interest to see what happened to the merocytes dur- 
ing all this. Nay more, the elucidation of their further history and fate 
became imperative, in view of what was shortly afterwards established 
for Lepidosteus, as will presently be recorded. 
Along with the yolk in the internal yolk-sac there were no mero- 
cytes found !); it was, therefore, concluded that they must be looked 
for in the external yolk-sac. 
And there, in fact, they are to be found. Soon after the critical 
period they begin to exhibit unhealthy characters, they shrink together 
and become smaller. They have, in the midst of plenty, a starved 
appearance, and their contents become much degenerated. 
Before the whole of the yolk has disappeared from the external 
yolk-sac, they have undergone a rapid degeneration, and their remains 
have fallen or crumbled away to form a sort of debris. 
It has long been known that shortly before hatching the contents 
of the yolk-sac are entirely drawn into the abdominal cavity and that 
the sac shrivels up. The details, which contain new facts, are as 
follows. 
By the time the embryo is 69 mm in length the yolk-sac has 
undergone considerable diminution, and when the embryo is 90 cm?) 
the external yolk-sac is a small flaccid bag, and, apparently, quite 
empty. 
The following table shows the dwindling in the external yolk-sac: 
length of . extension of yolk-sac 
Gags diam. of yolk-sac Ben body 
emb. 69 69 mm 10 mm 21 mm 
„er 40 SOs 5; 8 a 21 aE 
” 71 817, 1,5 „ 18 ” 
“rom SE 2 ir 6 5; 
) 68 90 „ 1 3) 2,5 bb) 
1) It may happen that a few merocytes do actually get drawn into 
the internal yolk-sac of Scyllium. I neither affirm nor deny it, and 
only state that I have found none. It would not, when one considers the 
remarkable facts to be described concerning their history in Lepidosteus, 
be surprising to find some of them in the internal yolk-sac (among the yolk) 
of Scyllium. 
2) At Naples the size of a newly hatched S. canicula is 10 em, 
according to P. Mayer. I have no means at present of determining if 
this be also the case in British specimens, but it is probably so. At the 
