12 
EMBRYONIC DEVELOPMENT 
side by side, in. transversal rows (figs. 7 and 7 a). The eggs are ejected in certain 
quantities, and maintained a while under the flat body of the animal, which secretes 
the mucosity and gives to them this peculiar arrangement; a short time afterwards 
the bands may be isolated from the surface upon which they were fixed, and the eggs 
will remain in their respective places. They may be seen distinctly through the 
transparent and hardened mucus, which now has the appearance of a thin leaf 
of whitish glue. The length of the bands themselves varies considerably, as the 
animal may be disturbed and compelled to recommence another one somewhat apart 
from the first. Sometimes the interruption is so often repeated, that instead of continu- 
ous bands, we have a series of irregular patches, in which the linear arrangement of the 
eggs is no longer observed (figs. 9 — 11). This is particularly the case towards the 
end of the laying ; the animal appears uneasy, impatient. It seems wearied from the 
labor of the spawning, and now takes no longer the same care of the last coming 
eggs. 
The number of eggs deposited by one individual is very great, as is generally the 
case amongst all the lower and unprotected animals. It will lay at repeated times a 
day, and so during a week or two, as the eggs develope successively. It is even a 
necessity for some to be expelled, before the following ones can reach the oviduct and 
complete their growth. 
There is but one yolk in each egg ; a single case was observed in which two yolks 
existed, giving rise to two embryos, still in full life during the period of the motion, 
when last observed. They were equal in size, and therefore one of them was not 
separated from the other, as in fig. 14, unless the separation took place by equal parts. 
Further on we shall witness a case in which, out of a unique sphere, two embryos is- 
sued, though by an accidental process of the living fabric. 
IV. 
THE LAID EGG. 
When observed immediately after they have been laid, the eggs are composed of 
the following parts : 1st, The yolk’s sphere, with the germinative vesicle in its middle; 
2d, A membrane surrounding the yolk or vitelline membrane; 3d, A zone of transpa- 
rent albumen, and 4th, An external membrane, analogous to the so-called chorion, en- 
closing and limiting the whole egg (figs. 12 and 13). 
The formation of the albumen and external membrane takes place during the pas- 
sage of the eggs out from the oviduct. Whether in the oviduct proper, in the coital 
pouch, or in the cloaca, I am not prepared to say just now, from direct observations, 
but feel confident that I may solve the question ere long, in the pursuit of my inves- 
tigations. 
o 
