ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
577 
The Blastopore in Meroblastic Ova.* — Herr N. Cholodkovsky seeks 
to unify the various forms of blastopore in meroblastic ova. In the cray- 
fish, the endodermic disc is surrounded by an annular groove and is 
gradually invaginated into the yolk. In birds, the homologue of the 
blastopore is the sickle-shaped groove from which the primitive groove 
extends forward. In Chalicodoma muraria , according to Carriere, the 
median part of the germinal area is bordered laterally by two furrows, 
which pass at either end into the originally superficial but subsequently 
invaginated endodermic rudiments. In Muscidae and in Phyllodromia, 
besides the primitive groove, there are two pairs of lateral furrows or pits 
which are separated by uninvaginated spaces, and seem rudiments of the 
complete annular groove of Astacus aud Chalicodoma. “ In Phyllodromia 
the primitive groove, extending from behind forwards, bears to the 
posterior pair of lateral invaginations the same relation that the primitive 
groove in birds bears to the sickle-shaped groove, which is probably the 
remains of an original annular groove. In Muscidse, the primitive 
groove which begins at the anterior end, bears a similar relation to the 
anterior pair of lateral invaginations, which are probably remains of the 
anterior half of the annular groove.” The broad and flat primitive 
groove of Hydrophilus recalls the lateral grooves in Apidae ; it is formed 
from lateral grooves which begin anteriorly and posteriorly, and repre- 
sent both halves of the original annular groove. The forms of primitive 
groove in insects are not all homologous. “ While the blastopore of 
Hydrophilus , Apis, and Chalicodoma is nearly related to the typical form 
in meroblastic ova, aud represents the entire endodermic disc of Astacus, 
the primitive groove of Muscidae and of Phyllodromia (like that of birds) 
represents only a median outgrowth of the rudimentary annular groove, 
and perhaps serves solely for the formation of mesoderm, the endodermic 
rudiments perhaps arising (as Graber suggests) from the complementary 
lateral invaginations. In some insects, therefore, the primitive groove 
represents the whole blastopore, in others only a part.” 
The Eggs and Embryos of the Crocodile.f— Dr. A. Yoeltzkow has 
studied these in Madagascar, where Crocodilus niloticus is very common. 
The egg-laying lasts from the end of August to the end of September. 
The number of eggs in a nest varies from twenty to thirty. The nest is 
dug about two feet deep in the dry white sand ; the bases of its walls 
are gouged out, and into the lateral excavations thus formed the eggs 
roll from the slightly raised centre of the nest-floor. Externally the 
nest is not discernible, but the parent sleeps upon it. The eggs differ 
greatly in form ; the shell is white, thick, and firm, either rough or 
smooth; the double shell-membrane is so firm that the egg keeps its 
form after the shell has been removed ; the albumen is a jelly firm 
enough to be handled, and the vitelline membrane is also very strong. 
When newly laid the eggs are very sensitive, and are readily killed by 
damp or by heat ; the older eggs, however, are quite hardy. When the 
young embryos are about to be hatched, they utter very distinct notes. 
These calls the mother hears, even through two feet of sand, and 
proceeds to dig open the nest. Even the natives were unaware of the 
* Zool. Anzeig., xiv. (1891) pp. 159-60 (1 fig.). 
t SB. K. Preuss. Akad. d. Wiss., 1891, pp. 115-20. 
