ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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well-authenticated appearance of diatoms to be in the Trias. While 
many species are cosmopolitan, others are known only within limited 
areas. 
Pearls of Diatoms.* — Prof. J. Brun claims to have settled the 
question that the pearls of diatoms are cavities and not protuberances, 
in the following way. If a particle of a transparent body immersed in 
a liquid is first exactly focused under the Microscope, and the tube then 
raised, the object will appear to have a bright centre if its index of 
refraction is higher than that of the liquid, a dark centre if the index is 
lower. If the tube is lowered the results are the opposite. If a diatom 
with large areas, such as a Coscinodiscus, is immersed in styrax or 
monobromide of naphthalin, and examined in this way, the pentagonal 
siliceous network is shown to have a lower index of refraction than the 
styrax, while the interior of the pentagon has not, showing that it must 
be a cavity, with the same index as that of the surrounding medium. If 
immersed in water, the inverse phenomenon is observed. 
Structure of Cyanophyceae.f — Herr H. Zukal has made a fresh 
study of several points connected with the structure and life-history of 
the Cyanophycese. 
In a large species of Oscillatoria he has detected, by sufficient 
magnification (1500-2000), in the peripheral portion of the protoplast, 
a distinctly fibrillar structure, although distinct grains were not dif- 
ferentiated. He concludes, therefore, that the Cyanophycem may, in 
certain cases, possess a highly organized chromatophore, although in 
others it is reduced simply to a coloured homogeneous parietal layer of 
protoplasm. 
With regard to the grains of cyanophycin, their position and distri- 
bution vary greatly even in different cells of the same individual. Their 
chief distinguishing characteristics are their solubility in dilute hydro- 
chloric acid, and the intense blue colour imparted to them by hsematoxylin. 
Their function in the economy of the cell is doubtful ; but their main 
purpose appears to be the formation of pigment. 
The “ red granules ” ( Schleimhugelri ) are not distinct in their origin 
from the grains of cyanophycin, since the author has been able, in one 
instance, to follow out the formation of the latter from the former. 
The central portion of ordinary vegetative cells, when mature, consists 
mainly of cytoplasm, with which glucose may occasionally be associated. 
It is not usually distinguished by a high refringency. It is readily 
fixed by absolute alcohol, and is then strongly erythrophilous. The 
author regards it as a soluble modification of the substance of the red 
granules, into which it is readily transformed. 
Although, under certain circumstances, a peculiar contraction of the 
entire protoplasmic contents of the cell takes place, there is not, in the 
Cyanophycem, any structure to which the term nucleole can properly be 
applied. 
In Cylindrospermum stagnate Herr Zukal has observed a remarkable 
process which he regards as a kind of conjugation. The cells contained 
* Le Diatomiste, ii. (1894) pp. 139-40. 
t Oesterr. Bot. Zeitschr., xliv. (1894) pp. 266-7, 281-6, 338-43, 387-91 ; Ber. 
Deutsch. Bot. Gesell., xii. (1894) pp. 256-66 (1 pi.). Cf. this Journal, 1894, p. 383. 
