ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
39 
cells at some length, and has a few notes on centrosomes and intercel- 
lular bodies. 
Excretory System of the Trout.* — Herr Felix describes the origin 
of the pronephros from five metameric evaginations of the lateral 
plates, in the third to seventh primitive segments. They correspond to 
other pronephric tubules, but there is no “ nephrotome” ; and they arise 
from both somatopleure and splanchnopleure. At the twelve-segment 
stage a pronephric fold arises anteriorly in place of the tubules, and 
posteriorly the caudal portion of the pronephric duct arises indepen- 
dently in the mesoderm. In the hatched trout the pronephros functions 
as the sole excretory organ. 
The pronephric fold becomes divided into a dorsal and a ventral 
portion by a fold ; from the dorsal portion is formed the cranial part of 
the pronephric duct; from the ventral portion, the pronephric chamber. 
The two portions are separated except at one point— the “ pseudo- 
pronephric tubule ” ; the dorsal part is shunted laterally, the ventral 
towards the middle. From a paired rudiment the glomerulus arises, and 
the pronephric duct opens behind the anus. 
The mesonej)hros arises, between the fifty-second and fifty-fifth day, 
by constriction from the pronephric duct, as five to nine spherical cell- 
masses successively separated off. From these there gradually arise the 
mesonephric tubules which break into the pronephric duct, about a 
month after hatching. They thus reunite with the duct from which they 
were originally constricted off. 
Between the posterior end of the mesonephros and the anterior end 
of the bladder, what the author calls the hind-kidney ( Nachniere ) arises, 
from an uncertain Anlage. There are 16-20 tubules, differing from the 
mesonephros in structure and position. They may be regarded, perhaps, 
as transitional phylogenetically to the metanephros of Amniota. 
Blastodermic Margin in Salmonidae.t — Herr Hs. Virchow discusses 
the concrescence-theory in an impartial manner; he finds that the 
direct metric (or volumetric) evidence breaks down, that the indirect 
volumetric evidence is inconclusive, and that though the morphological 
evidence lends the theory some countenance, the theory requires to be 
modified from its usual form. He is, however, exceedingly cautious, and 
declines to commit himself at present to any decisive statement as to the 
manner and degree in which the blastoderm margin in Salmonidsc is 
used in the formation of the embryo. 
Fertilisation of Egg of Amphioxus lanceolatus.J — Dr. J. Sobotta 
gives a preliminary account of his observations on the fertilisation of 
the egg of Amphioxus , of which as yet but little is known. It is generally 
supposed that the egg of Amphioxus is smaller than that of any other 
Vertebrate, but this is by no means the case. Its size varies not incon- 
siderably, but it is at least 100 p in diameter, and may be as much as 
130 p. Now the egg of the mouse is scarcely 60 p in diameter, and 
that of the guinea-pig is but little larger. The egg of Amphioxus is 
extraordinarily rich in yolk, while the quantity of protoplasm and of 
* Verb. Anat. Ges., ix. (1895) in Anat. Anzeig. Erganzungsheft, x. (1895) 
pp. 147-52. t Tom. cit., pp. 201-18 (9 figs.). 
X Anat. Anzeig., xi. (1895) pp. 129-37 (9 figs.). 
