3J2 



of Leydig's oells is generally small and Ilie3' are especially present 

 near the liiliis and there where three or more seminiferous tubules 

 come together. 



Till the end of January it was diffu-ull to distinguish the males 

 from the females, in the last days of January', however, one of my 

 specimens showed at throat and abdomen a faint black pigmentation, 

 which soon increased stronglj. Besides, this animal became very 

 agressive and in the beginning of February he began to collect 

 material for the nest. On the 14''' or 15"' of February the eggs were 

 laid in the completed nest; (I cannot give the exact date, as the 

 female was not seen in this nest). On the 16''' of February this 

 male was killed. 



The nuptial colours successively developed in the other males, 

 which soon began to prepare their nests. After the eggs had been 

 deposited in them, they were carefully guarded by the males, which 

 constantly conducted fresh water to the nests. 



On comparing the testes of animals killed in the end of Decem- 

 ber 01' in January with the testes of these males, we see that the 

 latter have greatly changed. 



The spermatogenesis has totally come to an end. The seminiferous 

 tubules are entirely tilled with a largp number of spermatozoa. 

 Moreover, at the periphery of the tubules small groups ot sperma- 

 tozoa are to be seen, the heads of which are directed to the wall 

 and the tails to the centre of the tubules. The number of sperma- 

 togonia and spermatocytes has strongly decreased. 



The interstitium is no longer narrow but is enlarged ; the number 

 of Leydig's cells has strongly increased ; the blood-vessels have become 

 more numerous and larger. 



So we see that the high temperature of the water in winter 

 favours the spermatogenesis and that consequently after four months 

 a testis originates of which the seminiferous tubules practically 

 contain spermatozoa exclusively. Then the secondary sex-characters 

 distinctly develop, the interstitium is enlarged and the cells of 

 Leydig and the blood-vessels increase in number. 



So I have observed a coincidence of the occurrence of the second- 

 ary sex-characters and the termination of the spermatogenesis, while 

 simultaneously an enlargement of the interstitium with increase in 

 number of the Leydig's cells and of the bloodvessels takes place. 

 This does not prove, however, that a correlation exists between 

 these phenomena. 



According to Courrier (1922a, 19226) it does. This investigator 

 observed in the three-spined Stickleback that after the spermato- 



4 



