ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
575 
from which the protoplasmic threads radiate. The author believes that 
the rounded bodies are the periplasts or centrospheres of Vejdovsky, and 
the central granules his centrosomes. At the time of the formation of 
the first directive spindle the centrospheres enlarge enormously and 
become coarsely reticular, within them the centrosomes are indistinct. 
The observations seem to prove that the large rounded bodies of the 
directive spindles of Vertebrate eggs are not centrosomes in Boveri’s 
sense, but centrospheres. 
Spermatogenesis in Man.* — M. Sappin-Trouffy describes two modes 
of nuclear division in spermatogenesis : — (a) a multiplication of cells 
by the usual karyokinetic process; and (b') a direct nuclear division or 
fragmentation of the nucleus into four. The latter is interpreted as a 
particular mode of chromatin reduction. 
Spermatogenesis in the Rat.f — Herr Ch. Regaud has attacked the 
problem of the origin of the spermatogonia in the mammalian testis. It 
is well known that the functional testis contains spermatogonia and the 
so-called “ cells of Sertoli.” The cycle of changes undergone by the 
spermatogonia has often been followed, but the question as to how the 
spermatogonia are renewed has received very insufficient attention. The 
author finds that in the rat the “ cells of Sertoli ” are really polymorphic 
nuclei imbedded in an undivided plasmodium. Their number remains 
nearly constant, but yet they increase by amitotic division. The resting 
spermatogonia consist of two main types. In the one the nuclei con- 
tain minute scattered granules of chromatin ; in the other the chromatin 
is in the form of fibres ; but complete series of transitional forms exist 
on the one hand between the nuclei of Sertoli and the nuclei with diffuse 
chromatin, and on the other between the latter and the nuclei with chro- 
matin rods. Close observation shows that the different forms have the 
following relations. In the first period all the spermatogonia are 
transformed into spermatocytes. Then certain of the nuclei of Sertoli 
surround themselves with cytoplasm, and become converted first into 
spermatogonia with granular nuclei and then into those with nuclear 
fibres. When a certain number of spermatogonia have originated in this 
way, those of the second type begin to divide by mitotic division, and 
are ultimately transformed into spermatozoa. Thus the spermatogonia 
arise from the “cells of Sertoli”; and as the latter multiply only by 
amitotic division this form of division cannot be regarded as invariably 
an indication of degeneration. 
Von Baer and Embryonic Variability.^ — Prof. Ernst Mehnert 
shows by quotations that K. E. von Baer fully recognised seventy -five 
years ago the fact of individual variation in embryonic development, 
and emphasised, furthermore, that the individual variations were physio- 
logical adjustments leading in the end to a normal embryo. He also 
maintained the position, recently reached by Fischel and Schwalbe, that 
the younger the embryos (of the chick) the greater are the individual 
differences. Mehnert complains of modern neglect of the older litera- 
ture, and gives some illustrations of this. 
* Comptes Rendus, cxxix. (1899) pp. 171-4. 
t Anat. Anzeig. (Erg'anzungsheft), xvi. (1899) pp. 42-57. 
X Biol. Centralbl., xix. (1899) pp. 443-55. 
2 Q 2 
