ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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two large ones, rich in starch. In the following spring the two nuclei 
unite, and the contents of the zygote escape from their membrane. 
Nuclear division then takes its ordinary course, and the zygote divides 
in two by a constriction in its middle, each half containing a nucleus. 
Each of these two nuclei again divides into two of unequal size, the 
larger, which has the character of a resting nucleus, with one or two 
nucleoles, becoming the nucleus of the new individual, the other, which 
has the character of a nucleole, disappearing. The germination of the 
spiny zygote of Cosmarium exhibits similar phenomena. 
It occasionally happens that three of the four nuclei resulting from 
the division pass into one of the two new individuals which are the 
product of germination, the other individual, which contains only one 
of the smaller nuclei, still undergoing complete development. The 
author observed also the germination of parthenospores, precisely resem- 
bling the zygotes except in their smaller size, each giving birth, like 
the zygotes, to two new individuals. The chromatic elements of the 
nuclei of the desmids are not filiform, as in Spirogyra, but granular or of 
the form of short rods, as in Ascaris ; and Herr Klebahn thinks it 
probable that in the complete process of impregnation, two fusions take 
place, one between the two nuclei of the conjugating cells, the other 
between the large and small nucleus of each cell. 
In the germination of other Conjugatae, species of Zygnema and 
Spirogyra , the unicellular product has only a single nucleus, which 
divides into two when the cell itself divides. 
Rhizoclonium.* — Herr S. Stockmayer reduces all the numerous 
species of Rhizoclonium described by various authors to five principal 
species, R. hieroglyphicum , fontanum, HooJceri, angulatum, and pachy- 
dermum, with numerous sub-species. He classes this genus, Chsetomorpha , 
and Cladophora together, as forming the family Cladophoraceae, nearly 
allied to Ulotrichaceae. Rhizoclonium is distinguished from Cladophora 
by the absence of true branching, from Chsetomorpha by the presence of 
rhizoids, though these are wanting in some of the slenderer forms ; but 
it is probable that some of the more slender species of Chsetomorpha 
should rather be assigned to Rhizoclonium. From Conferva and Micro- 
spora , Rhizoclonium differs in its reticulate chromatophores and the 
plurality of nuclei. 
M. F. Gay | regards the presence of rhizoids as the only character 
which can at present be used to distinguish Rhizoclonium from the allied 
genera Conferva and Cladophora. He finds the cells to contain one or 
two nuclei ; the zoospores escape through a lateral pore as in Cladophora , 
not by a circumscissile fissure through the middle of the cell as in 
Conferva and Microspora. 
Oogone and Oosphere of Vaucheria4 — Herr J. Behrens gives a 
careful description of the mode of formation of the oogone and oosphere 
in Vaucheria sessilis and geminata, confirming, in a general way, the 
account given by Berthold. The early stage of the formation of the 
oosphere consists in the detachment of the larger part of the protoplasm 
* Abhandl. K. K. Zool.-Bot. Gesell. Wien., xl. (1890) pp. 571-86 (27 figs.). 
f Journ. de Bot. (Morot), v. (1891) pp. 53-8 (4 tigs.). 
; Ber. Deutsch. Bot. Gesell., viii. (1890) pp. 314-8. 
