ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
753 
of the shell, especially the “extratlialamous ” materials for the daughter- 
shell, may become plastic. This plasticity makes secondary growth 
possible. The same conclusion is corroborated by all the investigations 
above mentioned. Therefore the opinion that these Rhizopod cases are 
permanently fixed when first established must be abandoned. 
Freshwater Rhizopods.* * * § — Dr. E. Penard gives a monographic ac- 
count of the freshwater Rhizopods which he has collected for the most 
part around Wiesbaden. In a general introduction he discusses many 
interesting problems — the shell-making, the structure of the plasma, 
the use of vacuoles as natatory vesicles, the direct relation between the 
activity of the contractile vacuole and that of the organism as a whole, 
the pre-eminent importance of the nucleolus and its variability (ten 
phases being described in Amoeba verrucosa ), the movements, the nutri- 
tion, the reproduction, &c. His observations corroborate, but do not 
greatly add to those of previous workers. In the systematic part of the 
memoir, which is illustrated by about a thousand figures, one hundred 
and ten species are described. There are eight new species of Amoeba , 
nine of Difflugia , four of Arcella , six of Nebela, and so on, the total of 
forty-seven making a notable addition to the list of freshwater Rhizopods. 
Biomyxa vagans.f — Mr. W. J. Simmons reports the presence in 
Calcutta of this amoeboid form described by Prof. Leidy from specimens 
collected in North America. 
Trypanosoma Balbianii.J — M. A. Certes finds that Trypanosoma 
Balbianii is generally abundant on the crystalline style of Tapes 
decussata, but it more or less completely disap pears when the style is 
dissolved. He has observed a large specimen undergoing horizontal 
division into two. In February and March 1891 the species had com- 
pletely disappeared from the green oysters of Marennes. 
Freshwater Peridine8e.§ — Herr A. J. Schilling has a monographic 
memoir on this group, in which, after a historical introduction, he com- 
mences by describing the organization of the creatures that compose it. 
One of the most puzzling parts are the so-called eye-spots or stigmata. 
They have the form of a polygonal or horseshoe-shaped disc, and are 
always placed in the longitudinal groove immediately beneath the surface 
of the body. As in the eye-spots of other Flagellata, the protoplasmic 
groundwork forms a fine network in which red-coloured granules or 
spherules are deposited. The speed with which these organisms move 
appears to depend on the size of the body. Reproduction appears to be 
always effected by vegetative multiplication by division into two. The 
statements that have been made as to processes of copulation and con- 
jugation want further confirmation. 
In the descriptive portion *of his work the author recognizes the 
six genera, Hemidinium, Gymnodinium, Amphidinium, Glenodinium , Peri- 
dinium , and Ceratium. He defines in detail the species that belong to 
each, some of which are new. 
* Mem. Soc. Phys. et d’Hist. Nat. Genev., xxxi. (1890-91) 230 pp. (11 pis.). 
f Sci. Gossip, 1891, pp. 199-202 (4 figs.). 
J Bull. Soc. Zool. France, xvi. (1891) pp. 94-5 (1 fig.). 
§ Flora, lxxiv. ( 1 891) pp. 220 99 (3 pis.). 
