ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
297 
deserved to be called dendritic, like those which Disse and Lenhossek 
have shown to occur in frog and bird. 
Nucleus of Ganglion-Cells and Neuroglia.* — Dr. Emil Rohde de- 
scribes the process of cell-increase in the ganglion-cells of Molluscs. 
Three different ways in which daughter-cells may arise from a ganglion- 
cell are described in detail, but these details cannot be readily condensed. 
A special point of interest is that in the first way the daughter-cells 
arise by separated portions of the nucleus of the mother-cell, surround- 
ing themselves with neuroglia, which, under nuclear influence, becomes 
transformed into ganglion-cell protoplasm. Rohde considers that this 
confirms the view of the supreme importance of the nucleus. 
Skin-Glands of Frog.y — Dr. Paul Junius has investigated the his- 
tology of these structures with a view to determining whether more than 
one kind=of skin-gland exists in the frog, and whether all the glands 
possess a muscular sheath ; both of which points are undetermined by 
previous authors. Junius’ conclusion is that only one kind of gland 
exists, the differences observed by various authors being due to the stage 
of development of the gland. He distinguishes two well-marked stages 
— (1) the embryonic stage, in which the gland is lined by a continuous 
secreting epithelium, and possesses but a few contractile cells not form- 
ing a distinct sheath, or a cell-layer of which the contractile nature is 
not distinctly marked ; and (2) a later stage, in which the lumen is com- 
pletely filled with secretion. In this stage some of the seereting-cells 
degenerate, and thus give rise to gaps in the wall of the gland ; while 
the pressure of the secretion and the presence of the well-developed 
muscular sheath quite alter the appearance of the gland. Junius was 
not able to completely satisfy himself as to the nature of regenerated 
glands, but holds it probable that these are of the embryonic type. 
Dentine and Enamel. i — Mr. C. S. Tomes has made careful analyses 
of dentine and enamel. Instead of stating that the former has 42 • 5 per 
cent, organic matter and the rest lime salts, we should say 34 per cent, 
organic matter and 8 • 5 per cent, water. Enamel, on the other hand, is 
“ practically an inorganic tissue,” the organic matter being infinitesimal 
in amount, though along with water it forms 5 * 49 per cent. 
Mr. Tomes makes an interesting comparison between the structure 
of enamel and the prismatic layer of a Pinna shell. Both show, for 
instance, a striation of prisms, probably due to regularly recurring vari- 
cosities. An analysis of a Pinna shell shows the following composition : 
Lime salts 89 • 2, organic matrix 1 • 3, water 9*5. “ The Pinna shell con- 
sists of crystalline prisms of calcic carbonate, containing no organic 
matter in themselves, but deposited in a honeycomb of connective tissue.” 
It seems a legitimate speculation, the author says, that enamel may be 
formed in somewhat the same fashion as the Pinna shell, “ namely, that 
the lime salts may be deposited in the interior of the enamel cells, and 
so a definite pattern produced, their exceedingly delicate walls playing 
the same part as the connective tissue honeycomb in the shell.” 
* Arch. f. Mikr. Anat., xlvii. (1896) pp. 121-35 (1 pi.). 
f Tom. cit., pp. 136-54 (1 pi.). 
j Trans. Odont. Soc., xxviii. (1896) pp. 114-36 (2 pis.). 
