ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
19 
after tlie teeth in front of it were also reduced. In relation to the 
back teeth, Kiikenthal finds evidence of no fewer than three successive 
dentitions taking part in the formation of the definitive tooth. The 
main mass is due to the first dentition, with its labial wall the prelacteal 
fuses ; the second dentition forms the rudiment of a lingual papilla. 
Development of Nostrils in Mammals.*' — Dr. H. Tiemann has 
studied this in various Mammalian embryos. Olfactory areas, thicken- 
ings of ectoderm in the front of the head, become pits and then pockets. 
There is no groove or furrow communicating with the mouth, nor does 
the maxillary process share in forming the primitive nasal cavity. The 
modification of pits into nasal cavities is mainly due to marginal growth 
and to epithelial fusion of the lateral and median nasal process. This 
epithelial fusion is replaced in the anterior region by a mesodermic 
mass which forms firm tissue ; posteriorly in the part towards the mouth 
the epithelial bridge persists for a time. But by separation of the side 
walls it becomes reduced to a thin membrane (membrana bucco-nasalis) ; 
and it is only when this at length ruptures that a communication between 
nasal cavity and primitive mouth-cavity is established. 
Spermatogenesis in Salamander.f — Dr. Fr. Meves follows the suc- 
cessive generations of sperm-cells in Salamandra maculosa. He begins 
with the period of multiplication, describing the spermatogonia at rest 
and during division. The period of growth is next discussed. The 
third chapter has to do with maturation. The first maturation-division is 
heterotypic, the second homootypic, and there is no strict resting-stage 
between. Both are equation-divisions, not reduction-divisions. We 
have not been able to summarise this elaborate paper, but in a general 
way it may be said that the account given brings the spermatogenesis 
of the salamander into line with that observed in other cases. There is 
much agreement with Flemming, and very complete disagreement with 
vom Bath. Apart from the particular theme and such particular results 
as the absence of any reducing division, the memoir includes much 
general discussion of the cell and its parts and the processes of mitosis. 
Influence of Light on the Pigmentation of Salamander Larvae.}: 
— Prof. W. Flemming comments on Fischel’s recent research as to 
the influence of temperature on the pigmentation of salamander larvae. 
Flemming’s observations, repeated year after year, show that the larvae 
kept in dark aquaria remain dark, while those exposed to light, e.g. 
in porcelain dishes, become light, the temperature remaining fairly 
constant. Flemming also notes that the processes of the pigment-cells 
may persist in contraction, though they escape observation. 
Segmentation of Nervous System in Squalus Acanthias.§ — Dr. 
H. Y. Neal has made a study of the neural segments and their relations 
to nerves in embryos of this fish, and he has been led to the conclusion 
that in it there exists in early stages a continuous primitive segmen- 
tation, serially homologous through the head and trunk. This is the 
neuromeric segmentation. In later stages there appears in the brain a 
* Verh. Phys. Med. Ges. Wurzburg, xxx. (1890) pp. 105-23 (1 pi.), 
f Arch. f. Mikr. Anat., xlviii. (1896) pp. 1-83 (5 pis.), 
j Tom. cit., pp. 369-74. 
§ Anat. Anzeijr., xii. (1896) pp. 377-91 (6 figs.). 
c 2 
