578 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
manner in which the attention of the mother is called to her young. 
Before hatching the embryo turns, and in so doing partially tears the 
foetal membranes. With the tip of its snout turned to one end of the 
egg, the young animal bores through the shell with a double-pointed 
tooth comparable to that which young birds possess. This tooth appears 
very early — by the time the embryo is six weeks or two months old ; it 
may still be seen a fortnight after hatching. Through the small perfor- 
ation made by the tooth the embryonic fluid flows out, softening the 
adjacent parts, and the whole is widened into a cleft. The process of 
creeping out may take about two hours. The young animal seems large 
in comparison with the egg ; thus one measuring 28 cm. in length came 
out of an egg 8 cm. long and 5 cm. broad. The young crocodiles are 
very wild little animals and are led to the water by the mother. They 
utter sounds, especially when hungry, but the pitch of their call is not so 
high as it was within the egg. Of the development, which takes about 
three months, some account is promised ; but the embryos are extraor- 
dinarily delicate and their investigation is proportionately difficult. 
Development of the Optic Nerves.* — Prof. A. Froriep finds from 
his investigation of the embryos of Torpedo ocellata that the first nerve- 
fibres of the optic nerve originate in the rudiment of the retina, whence 
they grow centralwards along the stalk of the optic vesicle. Keibel has 
observed the same in the embryos of Reptiles, but of this Froriep was 
unaware until he had completed his researches. 
Histogenesis of the Nenroglia.f — Prof. P. Lachi finds that there 
are two important periods in the development of the neuroglia of the 
chick’s spinal cord, — one limited by the 8th or 9th day of incubation, the 
other extending from this until the first few days after hatching. In the 
first period, the neuroglia is represented solely by ectodermic spongio- 
blasts ; in the second period these are joined by mesenchyme elements, 
which appear first in the white matter, but afterwards insinuate themselves 
into the grey. The new mesenchyme elements increase rapidly by 
indirect division, and towards the end of incubation they exhibit the 
prolongations characteristic of neuroglia cells. To these mesenchyme 
cells others of vascular origin — either endothelial cells or leucocytes — 
are added. From the twelfth day of incubation, Lachi observes the 
transformation and destruction of the spongioblasts, but their definite 
fate still requires investigation. 
Development of Blood in Embryonic Liver.J — Dr. O. Van der 
Stricht has studied the development of blood in the embryonic liver of 
representatives of various groups of Vertebrates. The hepatic cells 
themselves present special characters by which they may be easily 
distinguished from the adjoining blood-cells ; they are rich in fatty 
granulations, and their protoplasm has a reticulated structure. In the 
first stages of intra-uterine life the liver of Mammals has a close re- 
semblance to that of lower Vertebrates, and like theirs is formed of rows 
of hepatic cells arranged in a plexus ; later on a fresh capillary plexus 
is intercalated on the course of the one already present, and while the 
* Anat. Anzeig., vi. (1891), pp. 155-161 (12 figs). 
f Atti Soc. Tosc. Sci. Nat , xi. (1891) pp. 266-810 (3 pis ). 
X Arch. <lo Biol., xi. (1891) pp. 19-113 (2 pis.). 
