102 Transactions of the Royal Microscopical Society. 
in order to adapt itself to the form of the space which encloses it. 
Liberated from the egg and put in water, the body of the embryo, 
with the exception of the tail, straightens itself. Fig. 46 repre- 
sents one of these embryos under water, of the natural size ; Fig. 
47 represents an enlarged portion of it. How far these embryos 
were advanced in their development, the reader may judge himself 
from an examination of the drawings. I will only add that the 
greater part of the tissues still consisted of what we may call 
“ embryonal cells ” ; of course of different forms and diameter. 
The spinal column was just beginning to be formed. The circu- 
latory apparatus of the blood, as can he seen in the drawings, 
where the blood-vessels are represented in black, had very consider- 
ably advanced in development, for the rhythmical contractions and 
dilatations of the heart, represented by a prominence (Fig. 47) 
below the neck of the animal, were distinctly seen. The blood- 
vessels represented in black in the drawing, appeared in nature 
bright scarlet. While the head, neck, and posterior half of the 
body, owing to the commencing formation of the skin, was of a dark 
colour; the anterior portion, representing the future thorax and 
abdomen, was yellow, representing the remains of the vitellus, 
though abundantly supplied with blood-vessels. No trace of the 
development of the lungs or of any of the abdominal viscera could 
be discovered. The respiratory function was performed by two 
pairs of delicate leaf-shaped branchia, arising from the sides of the 
neck. Consisting entirely of large delicate embryonal cells, they 
were very transparent, offering not the slightest obstacle to the 
passage of the light during the study of the circulation of the 
blood. In fact, owing to the enormous size of the blood-cor- 
puscles, as well as to the transparency of the membranes, the 
corpuscles could be distinctly seen as they were swiftly passing 
through the vessels, even through the egg-membrane, with a 
1-inch objective, and illuminated with the daylight reflected upon 
the egg. The life of the embryos is very tenacious, for their blood 
may be seen still moving through the vessels of their branchiae six 
hours after they were removed from the egg and kept in water. 
By covering the eggs with a damp cloth, the embryos within may 
be kept alive for five or six days. 
As regards the blood-corpuscles of these embryos themselves, 
they have almost the same appearance as those of the fully- 
developed animal already described. The only difference to be 
noticed consists in a greater delicacy of structure, and in their 
smaller size, their long diameter amounting only to mm. ; 
their colour also is of a paler yellow. In some of these blood-cor- 
puscles I have observed the nucleus in the act of division. Treated 
with water, they distinguished themselves from those of the adult 
animal by not parting so readily with their colouring matter. 
