ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 263 



There are considerable individual differences among young specimens 

 of Lymn^ea. Of all the factors influencing growth nutrition is most 

 important. Of all the kinds of food the aiicrofiora is most favour- 

 able for growth. The volume and the surface area of the water have 

 only an indirect influence through the microflora. The number of 

 individnals pfeseut operates indirectly. The presence of excreta is 

 not injurious as Legendre maintained. In some cases it favours 

 arrowth bv favouring the multiplication of the elements of the micro- 

 flora. ■ J. A. T. 



Granular or Basal Cells of Ovotestis of Snail. — Luigi Cognetti 

 DE Martiis {Atti R. Acad. Torino, 19] 9-20, 55, 353-60, 2 figs.). 

 These cells are nutritive and phagocytic. The nucleus contains a very 

 large number of minute chromosomes, sometimes twinned or in pairs. 

 The meaning of this pairing is discussed. Attention is also directed to 

 numerous pointed fusiform intra-nuclear bodies, tlie meaning of which 

 is uncertain. J. A. T. 



Double Spermatozoa in Turritella communis. — Oh. Bataillon 

 {Gomptes Renclus Soc. Biol., 1921, 84, 219-22, 10 flgs.). The sperma- 

 tozoa are always in couples, united by a cytoplasmic pellicle around the 

 heads. This coupling is primitive and can be traced right through the 

 spermatogenesis. The cytoplasmic fission remains incomplete. But 

 there are two kinds of couples established in the first spermatocytic 

 division. They differ in the presence or absence of a heterochromosome. 

 They may be regarded as male-producing and female-producing. In 

 Turritella triplicata, studied by Schitz, the peculiarities above noted do 

 not occur. ■ • J. A. T. 



S. Lamellibranchiata. 



Experiments on Ovum of Cumingia. — L. Y. Heilbeunn {Biol. 

 Bulletin, 1920, 38, 317-39). The egg of this bivalve is surrounded by 

 a stiff vitelline membrane which tightly encloses the fluid cytoplasm. A 

 release from the restraint of this membrane is followed by maturation. 

 Such a release can be brought about in three ways— by membrane eleva- 

 tion, by membrane swelling, or by the removal or rupture of the mem- 

 brane. Substances which themselves have a low surface tension produce 

 a lowered surface tension of the membrane, and this results in its eleva- 

 tion from the egg surface. Acids, alkalies, and certain salt solutions 

 cause the vitelline membrane to swell. The membrane may be removed 

 from the eggs by shaking, or it can be made to rapture by immersion in 

 dilute sea-water. All these treatments produce polar-body formation. 

 All of them free the egg from restraint. Maturation in Gumingia 

 \> not dependent on an increase in oxidations. Cortical change in 

 Gumingia produces no increase in permeability either to dissolved 

 substances or to water. The essential features of cortical change 

 in Gumingia are the same as those which have been described in 

 Arhacia. J. A. T. 



