106 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE  [VOL. XI 
16 days than during any other period, although in one case in a mass 
of 156 eggs examined, after 18 days 80 of them still contained embryos. 
Before the hatching period, the median fin extends from the back 
of the head in a continuous line around the posterior end of the body 
and along the ventral surface forward to the yolk sac except where it 
is interrupted by the anal opening; the pectoral fins are developed also. 
The brain takes on much the structure of the adult brain, with the 
neural connection to eyes and ears; the nasal pits develop rather late. 
The heart becomes two-chambered but hangs rather loosely in the cavity 
in front of the yolk sac. The gill-slits make their appearance and the 
jaws are formed. The whole body remains transparent with the ex- 
ception of a few small, irregular black spots along the course of the 
alimentary tract. 
When hatched out the young herring is about 7 mm. in length and 
.75 mm. in depth including the fins, with a yolk-sac I mm. in length. 
The pectoral fins stand out quite prominently, but they seem to be but 
little used until the yolk is almost absorbed. In the newly-hatched 
salmon these fins are kept in rapid movement, apparently to assist in 
the aeration of the water, but in the herring they appear to have no 
such function in the early stages at any rate. The mouth is open, but 
the head is curved so that the mouth appears on the under side rather 
than at the anterior end. The gill slits are open, but as yet there are 
no cartilaginous supports for the arches. The alimentary tract is a 
tube of almost uniform size and appearance passing without convolu- 
tion from the mouth to the anal opening, which is situated well towards 
the posterior end of the body. The liver is represented only by a couple 
of tubules running for some distance parallel to the alimentary tract. 
The kidneys are present, although they do not show much development, 
but the ducts can be traced readily until they join and pass out just 
behind the anal opening in the same papilla. There is no sign of any 
vertebral skeleton forming around the notochord, but this has become 
extensively vacuolated, so much so, that except in sagittal sections 
scarcely anything can be seen but the walls. The muscle segments, 
however, are distinctly developed, showing the regular fibrillar struc- 
ture. The nasal pits are so near the undivided cerebrum that there 
seems to be scarcely any olfactory tracts, but the optic and the auditory 
nerves are well developed. The structure of the eye is practically the 
same as in the older forms, and in the auditory capsule the otolith, 
which is almost circular in cross section, is present. The optic lobes 
and the cerebellum are quite well developed. There is evidence of a 
pituitary body but none of a pineal body. The heart is not yet folded 
