ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
547 
pronephric chamber which was closed off from the abdominal cavity 
and contained a large glomerulus. The other funnel opened into the 
abdominal cavity. Sixteen or seventeen segments further back, the 
mesonephric tubules began, a pair in each of the following 16-17 seg- 
ments, each with the rudiment of a Malpighian body, and a short cellu- 
lar strand representing the beginning of a peritoneal funnel. 
The third stage showed the differentiation of the mesonephric tubules. 
There is a combination of Ganoid and Teleostean characteristics, the 
development of the mesonephros being more Ganoid-like, that of the 
pronephros more Teleostean-like. 
Development of Cerebellum in Teleostei. * — Dr. A. Schaper has 
studied the morphological and histological development of the Teleos- 
tean cerebellum in salmon and trout. It has a bilaterally symmetrical 
origin from a folding between the second and third embryonic vesicle ; 
the posterior limbs of these folds form the foundation of the cerebellum, 
the median portion does not grow so quickly, but by secondary infolding 
induces the formation of the characteristic valvuia cerebelli ; as a residue 
of the median groove, a narrow canal persists, running just beneath the 
surface of the cerebellum, and communicating anteriorly and posteriorly 
with the much reduced cavum cerebelli * but in most fishes there is in 
the cerebellum no “ central canal ” in the ordinary sense. As to the 
homology of the Teleostean cerebellum and that of higher Vertebrates 
there can be no doubt. 
There is no real distinction, such as His indicates, between “ Keim- 
zellen ” and epithelial cells. The “ Keimzellen ” of His are young or 
dividing ectodermic epithelial cells. At a certain stage, these begin to 
form indifferent cells, which migrate peripherally, and form both nerve- 
and glia-cells. The original epithelial cells form a transitory supporting 
framework ; only the ependym cells next the cavity persist. A transi- 
tory superficial granular layer arises wherever the typical cerebellar 
substance passes into a simple epithelial layer (ependym cells) or where 
the original epithelial layer persists. The superficial granular layer 
arises from indifferent cells ; its subsequent disappearance depends on 
a gradual migration centralwards of its component elements. As differ- 
entiation proceeds a certain number of indifferent cells are excluded 
from the metamorphosis, and remain as reserve-material. The whole of 
the neuroglia is ectodermic. 
Development of Fins of Teleostei-t — Mr. R. G. Harrison finds that 
the mesodermic structures of the median fins are formed from mesen- 
chyme cells derived from the sclerotome, and from muscle-buds which 
are outgrowths of either the dorsal or the ventral edge of the myotomes. 
These fins so far retain their primitive metamerism in that each muscle- 
bud may be traced directly into a certain muscle of each segment of the 
fin. The segmentation of the extreme anterior portion of the fins is 
secondary, although in the adult no difference can be seen between it 
and the rest. 
The ventral fins in the early stages of development likewise show 
signs of metamerism ; in these the buds soon disintegrate, and in the 
space occupied by them a single muscle-mass developes, the adductor 
* Anat. Anzeig., ix. (1894) pp. 489-501 (20 figs.). 
t Johns Hopkins Univ. Circ., xiii. (1894) pp. 59-61. 
