422 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



ment of the eggs of Pleuronectes platessa and Echinus esculentus. He 

 finds that the amount of variation from the normal concentration of 

 hydrogen and hydroxyl ions in sea-water which the eggs of the plaice 

 will tolerate is very small. A disturbance of the equilibrium towards 

 the acid side is much more fatal than the opposite. A progressive 

 development of resistance to unfavourable action of the environment 

 takes place in proportion to the age of the eggs. Phenolphthalein is 

 deadly to the eggs of the sea-urchin, but harmless to those of the plaice, 

 while dimethyl quickly kills the latter, and appears, if anything, to have 

 a favourable influence upon the development of the former. 



Artificial Parthenogenesis.* — Yves Delage points out that the mode 

 of action of the various agents which induce artificial parthenogenesis is 

 still uncertain. Diverse methods have similar results, and no one is 

 effective in all cases. Even an osmotic pressure greater than that of the 

 sea-water, which is usually very effective, is not indispensable, for 

 Delage's experiment with starfish ova, subjected to the influence of 

 carbon dioxide in diluted sea-water, " hypotonic " in relation to the 

 normal sea- water, was successful. Much seems to depend on the 

 variable condition of the eggs themselves, and on the temperature of 

 the medium. Acidification is favourable to parthenogenesis in the ova 

 of starfish, unfavourable in the case of the sea-urchin (Strong ylocentrotus). 

 The mixture which gave best results was thus composed : sea-water, 

 3 c.cm. ; solution of pure NaCl, 45 c.cm. ; distilled water, 72 c.cm. ; 

 sulphite of soda, 5 drops. Delage has reared plutei which lived for 

 2-6 weeks, and one of the starfish larvae obtained by the carbon-dioxide 

 treatment lived for over four months. 



Maturation and Fertilisation in Porpoise.j — W. Eubaschkin notes 

 that the guinea-pig has an ovulation soon after parturition, and may 

 then be inseminated. If copulation does not occur the vagina closes 

 till the next oestrus. The maturation is for the most part in the ovary. 

 Two polar bodies are always formed. After the appearance of the 

 second directive spindle, the ovum passes into the Fallopian tube, where, 

 or in the lower part of the oviduct, fertilisation takes place. The 

 process of fertilisation is described. 



Oolemma of Mammalian Ovum. J — A. Fischer describes the 

 oolemma of the mammalian ovum as a product of the epithelium which 

 surrounds the ovum ; its growth is from within outwards in peripheral 

 layers ; it is a spongy, homogeneous sheath formed of a feltwork of 

 threads from the epithelial cells ; and it is penetrated until the period of 

 maturation by fine processes connecting the epithelium with the ooplasm 

 and playing a nutritive role. 



Individuality of Chromosomes.§ — R. Fick has subjected to a 

 searching criticism the whole framework of conclusions in regard to 



* Comptes Rendus, cxli. (1905) pp. 1201-4. 



t Anat. Hefte xxix. (1905) pp. 503-57 (4 pis.). See also Zool. Zentralbl., xiii. 

 (1906) p. 215. 



X Tom. cit., pp. 555-89 (1 pi.). See also Zool. Zentralbl., xiii. (1906) p. 214. 



§ Arch. Anat. Physiol. (Anat. Abth.) 1905, pp. 179-225. See also Zool. 

 Zentralbl., xiii. (1906) pp. 206-7. 



