324 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Median Groove of Triton.* * * § — Prof. C. Van Bambeke finds that in 
Urodeles, and especially in Triton alpestris, the median, or dorsal, groove 
is a vestige of the primitive groove. It may be admitted, with Hertwig, 
that this median groove represents the line of suture along which the 
lips of the blastopore became fused ; and it is, therefore, comparable to 
what Hatschek called the gastrular raphe in Ascidians, Amphioxus , 
and Annelids. If this be correct, we may say that the mesoblast on 
either side of the groove is a peristomial mesoblast, in the sense of 
Babl ; and this is the view almost simultaneously taken by F. Keibel, 
who has been investigating the development of the domestic pig.f No 
less than the evidence brought forward by 0. Hertwig and DavidofF, 
that afforded by the history of T. alpestris favours the theory of concres- 
cence. 
Fecundation of Egg of Trout.J — Prof. H. Blanc has had the oppor- 
tunity of making some experiments on the artificial breeding of Trutta 
lacustris. He finds that the germinal vesicle does not disappear towards 
the end of the maturation of the egg, but is transformed into a polar 
spindle even while the egg is contained in the abdominal cavity. The 
first polar globule is expelled as soon as the egg leaves the body. On 
contact with water the germ and yolk execute movements which, though 
slight, and short in duration, suffice to vary the position of the nucleus of 
the egg in relation to the micropyle. Fertilization takes place half a 
minute after the commingling of the sexual products ; it is rare for more 
than one spermatozoon to enter. At this time the second spindle pre- 
pares for the expulsion of the second polar globule and the elaboration 
of the attractive sphere of the female pronucleus. The maturation of 
the egg is not complete till the two attractive spheres have been elabo- 
rated by the two sexual nuclei. 
The fact that the two polar globules are expelled from non-fecundated 
eggs, shows that fertilization has nothing to do with the phenomenon. 
Although the protoplasm of the germ of the egg may play the part of a 
nutritive structure to the pronuclei, it does not remain indifferent to the 
centres of the future attractive sphere, which rapidly find in it the con- 
tractile elements which allow of their playing their “ dynamic role.” 
The male and female pronuclei are attracted towards one another 
with equal intensity by the attractive spheres, but it may happen that 
one of them acts for a moment with the greater intensity. When the 
attractive spheres have fused, and although the nuclear membranes have 
disappeared, the identical contents of the two pronuclei do not at once 
mix. This, however, is effected, and there results a nucleus with a 
single reticulum enclosed in a distinct membrane. 
In cases of polyspermy it is the first spermatozoon which succeeds 
in penetrating into the micropylar canal that alone is transformed into 
the male pronucleus. 
Vertebral Column of Ganoids.§ — Herr C. Hasse, in his fifth com- 
munication on the development of the vertebral column, discusses the 
* Arch, de Biol., xiii. (1893 [published 1894]) pp. 147-62 (1 pi.), 
t Cf. p. 123 of Morphol. Arbeiten, iii. (1893). 
t Ber. Naturf. Gesell. Freiburg i/B, viii. (1894) pp. 163-91 (1 pi.). 
§ Zeitschr. f. wiss. Zool., lvii. (1893) pp. 76-96 (2 pis.). 
