311 



dilcliwater in spring (12° — 20° C), would liave on tlie a|tpearance of 

 tlie secondary sex-cliaraoters and wliat clianges would take place 

 in the testes of these animals simullaiieouslj. The sex-glands of 

 control-animals, caught in nature, could serve at the same time to 

 verify the results of Courrier. Iu this paper I will onl}- communi- 

 cate the results, obtained in animals, kept in a temperature of 

 12'— 20°C. during last winter. 



In September and October 1922 I caught a large number of 

 specimens of Gasterosteus pungit/us L. at Rotterdam. They were 

 kept in an aquarium of which the water was often renewed, ami 

 they were copiously fed with Chiro7iomus-l&vvsie. 



All the testes of the Sticklebacks, killed in autumn, contained a 

 more or less large number of spermatozoa. The number of sperma- 

 togonia is always small, the number of spermatocytes and sperma- 

 tids varies in the different specimens. In all cases, examined by nie, 

 small groups of interstitial cells (Leydig's cells) were present, close 

 to the hilus or there where three or more tubules come together. 

 In a few testes, in which the interstitium is somewhat wider, these 

 cells are also situated between the seminiferous tubules. They were 

 absent in none of the cases examined. 



In one specimen (n°. 6), a rather dark-coloured male, not showing 

 the black pigmentation of males during breeding time, however, the 

 interstitium is much wider than in the other males, caught at the 

 same time. The number of interstitial cells is also larger in this 

 specimen, while iu the seminiferous tubules spermatozoa are almost 

 exclusively found. 



Oblong connective tissue-nuclei are observed everywhere in the 

 interstitium of the testes of animals, caught in autumn , blood-vessels 

 are present, but they are not numerous ; they are narrow and contain 

 few blood-cells. 



This testis-structure is shown by animals, caught in September and 

 the beginning of October, and which were kept in an aquarium of 

 wliich the water then agreed in temperature with ditchwater. 



The testes of Sticklebacks, kept for two, three and even four 

 months, i. e. till the end of January 1923, in a temperature of 

 12° — 20° C, all increase in size and show the following structure. 

 The spermatogenesis is very intensive. In all testes this process 

 takes [ilace from the exterior to the interior, i. e. the spermatozoa 

 are situated as a rule more in the centre, the spernuitogouia and 

 spermatocytes more at the periphery of the gonad. The interstitium 

 of such animals does not change; it remains narrow, the number 



