ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
549 
Development of Ampliioxus.* — Herr J. Eismond agrees with those 
who doubt the primitive nature of Amphioxus. He begins by referring 
to what Kowalevsky and Hatschek have made certain, that before the 
medullary rudiment becomes a groove it is overgrown in epibolic fashion 
by a kind of ectodermic skin. This grows forwards from the lower lip 
of the blastopore and the adjacent posterior lateral regions of the ecto- 
derm. Hatschek’s account is, however, more accurate than Kowalevsky’s. 
The overgrowth is quite distinct from the closure of the medullary 
groove, and if Amphioxus be primitive what of this overgrowth-process 
in higher Vertebrates ? The author explains the difficulty of bringing 
the development of the lancelet into line with that of higher Vertebrata, 
and his solution is this : — 
The dorsal invagination in Amphioxus must be regarded as homo- 
logous with that in Selachii and Amphibia, while the persistently growing 
marginal zone of the formative germinal area corresponds with the over- 
growing margin of the blastoderm in Fishes and Amphibians, where the 
overgrowth spreads over the vegetative portion. In short the over- 
growing in Amphioxus is to be derived from an epibole such as occurs 
in these other forms. Eismond supposes that the ovum of Amphioxus 
is secondarily poor in yolk, like that of placental mammals, and that 
the overgrowing in Amphioxus is homologous with the spreading of the 
blastoderm in Fishes and Amphibians, with this difference that the 
absence of yolk-ballast causes the growth to take place dorsally. 
j3. Histology. 
The Cell and the Animal Tissues.! — Dr. E. S. Bergh published 
(in Danish) a book on the Cell and the Animal Tissues at the same time 
as Prof. Hertwig published his similar work. There is now a German 
edition of Bergh’s book. It differs from Hertwig’s analogous work in 
the subordination of physiological considerations, in taking less account 
of what is still very hypothetical, and in classifying tissues on a basis of 
comparative histology rather than on embryological considerations. All 
forms of tissues are linked by intermediate types, all are traceable to 
epithelium, but a classification according to the germinal layers from 
which they arise is not accepted. 
Number of Chromosomes in Animal-cells. :f — Dr. 0. vom Eath de- 
scribes a sufficient number of cases to show that one cannot always 
expect to find in the nuclear spindle the number of chromosomes 
characteristic of the species. Though the result reached by Flemming 
and Eabl, which many others have corroborated, that there is for each 
species a typically constant number of chromosomes, remains generally 
true, vom Eath notes the occurrence of double, quadruple, and multiple 
chromosomes, and observes also that a chromosome may divide up into 
units of a lower order. In determining the number of chromosomes 
typical of the species, the mitoses of epithelial and endothelial cells are 
most important ; modifications are most likely to occur in the sex-cells, 
cleavage-cells, embryonic cells, and blood-cells. Of some of these 
modifications descriptions and analyses are given. 
* Biol. Centralbl., xiv. (1894) pp. 353-60 (1 fig.). 
t ‘ Vorlesungen iiber dieZelle und die einfaclien Gewebe des tierischen Korpers. 
Mit einem Anhang, technische Anleitung zu einfaclien histologischen Untersuch- 
ungen,’ Wiesbaden, 1894, 8vo, 262 pp. and 138 figs. See Biol. Centralbl., xiv. (1894) 
pp. 478-80. X Biol. Centralbl., xiv. (1894) pp. 449-71 (19 figs.). 
