310 



a iminher of seoondai'v sex-cliaraclers (cf. Titschack 1922), of wliicli 

 tlie following are distiiictlj' perceptible. 



In spring a very distinct black pigmentation (red in the tliree- 

 spined species) can he observed at tlie throat and at tiie abdomen, 

 which soon spreads over the rest of the body, so tliat tiie animals 

 become dark-black, except for their pectoral spines. Outside 

 breeding-time it is difficult to distinguish the males from the females: 

 then both show dark spots on a pale green ground. Individual 

 colour-differences occur. 



Every male makes a nest, in which the eggs are deposited. The 

 material of which the nest consists (parts of waterplants etc.) is 

 collected by the male and fastened by means of a secretion, formed 

 by the kidney-lubules and Wolffian Ducts (Titschack 1922, Coukrikk 

 19226, both in Gasterosteus aculeahis L.). This peculiar secretion 

 occurs exclusively in the male during breeding time ; for that reason 

 in spring the kidney strongly increases in size, the kidney-tnbules 

 and the Wolffian Ducts get a larger diameter and exercise a different 

 function. 



The male guards his nest and drives off all intruders fiercely. When 

 the eggs have been deposited in the nest, they are at once fertilized. 

 During the development of the eggs, the male takes care that they 

 are constantly provided with oxygen by conducting fresh water to 

 the nest with his pectoral fins. Sometimes, when eggs drop out of 

 the nest, they are again collected by the male and taken back to 

 the nest in his mouth. Whether the young are guarded by the male, 

 after they have left the nest, in nature, is not known to me: care 

 must be taken to separate the young, living in prison, from their 

 father and the other inhabitants of the aquarium, as the young 

 will otherwise be eaten. 



The aim of my investigation, l)egun in September 1922, was to 

 trace the changes, occurring in the testes of the Stickleback at the 

 appearance of the secondary sex-characters. So it was my intention 

 to catch a number of Sticklebacks at fixed times during the winter 

 and the succeeding spring and to examine their sex-glands. At that 

 time I thought that nothing was known as yet about the relation 

 between the secondary sex-characters and the testis of the Stickle- 

 back, but it soon appeared to me that Courrier had already investi- 

 gated the three-spined Stickleback [Gasterosleus nculeatus L.) and 

 had published some papers, i-egarding this point (1922rt, 19226). 



I therefore changed my original plan and resolved to trace what 

 influence a rather high temperature, about the temperature of 



