ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
435 
always show that they have only served to bring some preformed adapta- 
tion into activity.” 
Yolk-nuclei in Meroblastic Ova.* * * § — Prof. H. E. Ziegler discusses 
these bodies as illustrations of nuclear degeneration. He believes still, 
as he did some years ago, that they are elements left behind in the 
development of the embryo. In Torpedo he is quite convinced that from 
the beginning of gastrulation the “ meganuclei ” take no part in the 
formation of the germinal layers. He discusses some of the interpreta- 
tions of the yolk-nuclei, all of which, his own included, leave one with 
the impression that not very much is certainly known about them. 
Fertilization of Trout’s Ovum.| — Frof. H. Blanc finds that the 
formative “germ” is present in the ovum before submergence and 
that fertilization has nothing to do with its appearance. The germinal 
vesicle does not disappear towards the end of maturation ; a polar spindle 
is formed while the ovum is still in the abdominal cavity ; the first polar 
body is expelled immediately after laying. In contact with the water 
the contents of the egg (germ and vitellus) exhibit certain movements 
which alter the position of the nucleus in relation to the micropyle. 
Fertilization occurs half a minute after mixing the elements, polyspermy 
is exceptional, but not pathological. The second polar spindle gives 
rise to the second polar body and to the attractive sphere of the female 
pronucleus. Maturation is only completed when the two nuclei have 
each their attractive sphere. Unfertilized eggs form two polar bodies ; 
the process is quite independent of fertilization. The pronuclei come 
together 9-10 hours after fertilization; the attractive spheres fuse; 
the nuclear membranes disappear; the segmentation nucleus is formed. 
The first cleavage is in a plane perpendicular to the equatorial plane in 
which the segmentation spindle lies. Thus Prof. Blanc has confirmed 
in regard to trout some of the general results of recent studies of fer- 
tilization. 
Development of the Teeth in the Adder. J — Dr. C. Rose describes 
the origin of the dental ridge and the appearance of the tooth-germs. 
As in other Reptilian embryos, there are on the premaxilla two germs of 
“ egg-teeth.” The same bone bears rudimentary germs of other teeth. 
Ten rudiments of fangs were observed. As to the structure of the teeth, 
Tomes was right in maintaining the presence of a thin layer of enamel ; 
it extends from the cap downwards as far as the tooth projects from 
the mucus-membrane. As in Crocodilians and Chamseleons, there is a 
transitory enamel-pulp with stellate cells ; it lies in the poison canal 
and disappears. The origin of the various layers of the tooth are care- 
fully described. 
Development of Excretory System in Amphiuma.§ — Mr. H. H. 
Field finds that the rudiment of the mesonephros in Amphiuma is strictly 
metameric, as in Csecilians. There is a subsequent irregular duplication 
of the nephrostomes and nephrostomial canals in the anterior segments 
of the kidney. The canalis principalis remains undivided, while the 
canalis nephrostomialis is doubled. 
* Ber. Nat. (4es. Freiburg, viii. (1894) pp. 192-209 (4 figs.). 
t Tom. cit., pp. 163-91 (1 pi., 1 fig.). 
X Anat. Anzeig., ix. (1894) pp. 439-51 (10 figs.). 
§ Comptes Rendus, cxviii. (1894) pp. 1221-4. 
