ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
187 
“radial fibres.” With these, as His has shown, the nerve-cells have 
nothing to do, for they arise directly from mitoses of the germinal 
layer, and are new additions to the primary supporting system. Len- 
hossek describes the origin of the motor neuroblasts in the anterior 
horns of the cord, tracing them outwards from the germinal layer. The 
membrana prima or membrana limitans externa is due to a mosaic-like 
union of the terminal plates of the radial cells, and readily admits of the 
outgrowth of nerve-fibres from the cord. As early as the third or fourth 
day of incubation, the neuroblasts begin to give off processes, and become 
nerve-cells. The diiferent layers of the cord then begin to be differen- 
tiated. The author traces the origin of the commissural cells and of 
the anterior horn. His conclusions are important corroborations of 
those already reached by His and Ramon y Cayal. 
Development of Oviduct of Frog.*— Mr. E. W. MacBride in inves- 
tigating the development of the oviduct in the Frog, found that it was 
necessary to use tadpoles in which the tail was being absorbed, or had 
just vanished. He finds that the oviduct arises opposite the first and 
not the third nephrostome of the pronephros ; the whole of the duct 
arises in connection with a strip of modified peritoneum, and apparently 
by proliferation from it, and it is entirely independent of the Wolffian 
duct. The lumen of the duct appears quite close to the peritoneum, and 
in patches. These facts seem to show that the whole oviduct of the 
Frog is a production of the peritoneum; a somewhat similar view has 
been taken by Wiedersheim as regards the Crocodile and Turtle. 
The ordinary view that the oviduct is part of the primitive prone- 
pbric duct is founded on what happens in Elasmobranchs, but in 
Ganoids, Amphibia, and Reptiles — groups which probably approximately 
represent stages in the actual line of descent of Vertebrates — the oviduct 
seems to be derived from a dorsal groove in the peritoneum. 
Precocious Segregation of Sex-cells in Micrometrus aggrega- 
tus.f — Mr. C. H. Eigenmann has discovered that the sex-cells of this 
Teleostean can first be distinguished from the surrounding cells about the 
time the blastopore closes. They dilfer from those around them by 
having well-defined, rounded outlines, and in the uniform distribution of 
the chromatin in small granules. The appearances in later stages are 
described, and the suggestion is put forward, that the present position 
of the gonads in the Craniata is not the primitive one, but that the 
anterior gonads of Branchiostoma ( Amphioxus ) probably represent the 
earlier condition. From this forward position the germinal region 
has been extended backwards, the anterior part undergoing atrophy 
later on. 
Development of Batrachus Tau.J — Miss C. M. Clapp has a few 
notes on the development of the Toad-fish. This Teleostean exhibits an 
interesting Elasmobrauch character by the delay of the closure of the 
blastopore, in consequence of the great amount of food-yolk ; a notched 
blastopore, at a distance behind the embryo, has not till now been known 
in Teleosteans. 
* Quart. Journ. Micr. Sci., xxxiii. (1802) pp. 273-81 (2 pis.). 
t Journ. Morphol., v. (1891) pp. 481-92 (1 pi.). 
j Tom. eit., pp. 494-501 (3 figs.). 
