341 
8UMMARY OF CURRENT RESEARCHES RELATING TO 
out from the ova. In fact, each sphere of jelly is a little incubator. 
Figures relating to the physical demonstration of this are given. 
Among other interesting facts, it is noted that the spawn sinks in water 
in which there are no plants, but is in normal conditions buoyed up by 
the gas-bubbles liberated from water-plants. 
Maturation, and Fertilization of Trout Ova.* * * § — Dr. H. Blanc finds 
that in the maturation of the ovum of the trout ( Trutla lacustris ) two 
polar bodies are extruded, and a “ solar centre ” accompanies the female 
pronueleus. The spermatozoon when transformed into a male pro- 
nucleus has also its solar centre. In fertilization, the two pronuclei 
fuse, and so do their solar centres. 
Gonads of Amphioxus.f— Dr. Th. Boveri finds that the somites of 
Amphioxus, from 10-35 or 36, include not only a myotome and a sclero- 
tome, but. a third definite part — a “ Gonotome.” This may be defined 
as a definite ventral portion of a somite, bounded by anterior, posterior, 
medial, and lateral walls. The two last pass ventralwards into one 
another. Dorsally the gonotome i6 in open connection with the united 
sclero-myotome. The medial wall is continued into the skeletogenous 
layer of the sclerotome, the lateral into the cutis-layer of the myotome, 
while the anterior and posterior walls are continued into the muscle- 
septa. When somite and lateral plates are still one, the gonotome — as 
the most ventral part of the somite — must border directly on the lateral 
plates. But this definition holds good for the nephrotomes or gonone- 
phrotomes of Craniota, which in their ventral regions contain the primi- 
tive reproductive cells. The gonotome of Ampliioxus is homologous 
with the gononephrotome of Craniota, and the archinephric canals 
of the latter correspond to the genital chambers of Amphioxus. 
Nutritive Importance of Yolk-sac.} — Dr. A. Robinson, who has 
made observations on the mouse and the rat, comes to the conclusion 
that in Rodents, as well as in Insectivora and Marsupials, the yolk-sac 
is an important nutritive organ. In the rat and mouse, indeed, the 
yolk-sac is the only foetal organ of nutrition during a certain period of 
development. The author thinks that the almost constant appearance 
of the hypoblast iii the placental area, and the fact that it enters that 
area from different situations in different animals are indications of its 
functional importance during intra-uterine development : the hypoblast 
is not merely a framework which carries the splanchnic mesoblast on its 
expanding surface, and brings it into contact with the trophoblast, but 
it is an active agent of considerable importance during the later periods 
of development. 
Formation of Peripheral Nervous System of Vertebrates.§ — M. 
P. Mitrophanow, thinking that too much stress has been laid on the 
lessons learnt from the development of the Chick, has made his funda- 
mental observations on Selachians. In them he finds that the edges of 
the medullary plate first come together in the region of the hind- and 
* Bull. Soc. Yaud. Sci. Nat., xxvii. (1892) pp. 272-5. 
t Anat. Anzeig., vii. (1892) pp. 170-81 (12 figs.), 
j Joum. Anat. and Pliysiol., xxvi. (1892) pp. 208-23(1 pi.), 
§ C-jmptc-8 Rendns, cxiii. (1891) pp. 659-62. 
