348 SUMMARY OF CURRENT RESEARCHES RELATING TO 



It is suggested that the conditions determining fche appearance of inter- 

 stitial cells in the ovary hold also for the testis. 



Sex-ensemble.* — I). Berry Hart defines sex with primary ivfereiuv 

 to the nature of the sex-gland. The nature of the duct system alone or 

 of the secondary sexual characters does not enter into the strict definition. 

 A typical sex-ensemble includes a normal sex-gland, a developed duct 

 system characteristic for the sex, an opposite sex-duct element in a 

 degenerated condition, and a secondary sexual series of characters con- 

 gruent with the sex. The normal duct system should be at a maximum, 

 the opposite sex-duct element at a minimum. In atypical forms the 

 normal sex-duct segments are diminished in number, the opposite sex- 

 duct elements increased, and the secondary sexual characters non- 

 congruent. Any of the units of sex-ensemble may be inverted, and this 

 is an intrinsic result. The sex-ensemble is determined by the gametic 

 determinants. The gametes only determine the sex-duct element. It 

 is the primitive germ- or sperm-cells, formed shortly after the zygote 

 arises, that, travelling through the germ-layers and entering the sex- 

 gland, give rise to sex. The nature of the germ-cells in the sex-gland, 

 and that of the potent, non-potent, and congruent secondary sexual 

 characters gives the sex-ensemble. Intrinsic changes in the germ-plasm 

 give rise to variations, and mutations, in particular, are to be associated 

 with loss of polar bodies, maturation, and the formation of gametes. It 

 is suggested that the determinant of the evolutionist becomes more 

 intelligible when conceived of as comparable in behaviour to the atom of 

 the physicist. 



b. Histology- 



Epidermis of Amphibians Cultivated Outside the City.t — S. J. 

 Holmes continues his investigations on pieces of tissue cultivated in 

 lymph and plasma.^ His observations on the movements of isolated 

 melanophores have been recently summarized. § Most of his recent 

 experiments relate to the epidermis of the larva? of Diemyctylus torosus, 

 and the pieces were cultivated in lymph or plasma. 



The epidermis of amphibian lame grows well in a mixture of equal 

 parts of a 2 p.c. gelatin solution and blood serum from the adult 

 animal. Epidermis shows a marked thigmotaxis, and in hanging drop 

 cultures extends away from the implanted tissue along the lower side of 

 the cover slip and the lower surface of the drop of culture medium. 

 The extending mass of epithelium usually takes the form of a broad, 

 thin sheet, whose outer border is formed of very thin clear protoplasm 

 furnished with fine pseudopoclia. 



Sheets of extending epidermis are sensitive to slight stimulations, and 

 show a remarkable degree of contractility, often drawing in to a small 

 fraction of their previous superficial area. Strong contractions of 



* Edinburgh Med. Journ. (June, 1915) pp. 1-21. 

 t Journ. Exper. Zool., xvii. (1914) pp. 281-94 (1 pi.). 

 t See this Journal, 1914, p. 245. ' 

 § See this Journal, 1915, p. 133. 



