27 
egg-capsule does the yolk appear to be digested by the alimentary 
tract of the Elasmobranch. 
In Anguis, according to Hans VırcHOw, the remains of the yolk- 
sac would appear to be cast off. 
In the discussion on my paper a personal friend hinted that I 
had been led to look upon the yolk-sac as part of the larva from 
having followed some “stray ends of larval nerve fibres” on to that 
structure. I had to confess my regrets that at that time I was unable 
to lay claim to any such observation, indeed, that having cut my em- 
bryos of Rajabatis without any part of the yolk-sac appended, it 
had never occurred to me that the fibres described might pass to the 
yolk-sac. Quite recently it has been seen that at any rate some of 
the larval subepiblastic nerves of the Anat. Anz. paper 
do undoubtedly make their way to the surface of the 
yolk-sac, lying in their course just beneath its epi- 
blastic covering. That a further confirmation of my conclusion 
is to be found in this observation goes without saying. 
Fate of the ‘Larva in Mammalian Development. 
Some three years ago when considering the „Interrelationships of 
the Ichthyopsida”, at a time when this larval question was promi- 
nently before me as a fascinating puzzle, | imagined that the larva 
disappeared above the Ichthyopsida. I was led to this conclusion — 
by reliance on the accepted belief that larvae are only met with in 
aquatic and, more particularly, marine forms, and by the apparent ab- 
sence of a larval nervous system above the Ichthyopsida. My 
recent studies and the work of FRORIEP and Ropinson have taught 
me that this was erroneous. 
The larva never disappears, however much it may 
undergo degeneration. 
It may even be doubted if there are not traces of the nervous 
apparatus of the larva in the ontogeny of the Amniota, for there 
appear to be certain observations of FRORIEP on Reptiles, which may 
admit of interpretation in this sense, and my friend, Dr. ARTHUR 
Rosgrnson, tells me that he believes he has found traces of it in cer- 
tain Mammalian embryos. 
In Mammals, as will be seen, the larva must be regarded as an 
internal parasite, and like such it would yield up its chief organs. 
Some traces of its nervous system may, however, persist, as I have 
proved to be the case in Mustelus vulgaris, where the larva is 
almost as parasitic as in the Mammal. 
The amnion of the higher Vertebrata is probably also a larval 
