FISHES 219 



Ireland in which the pelvic spines were absent altogether. 

 He does not state whether these were females. 



In the Sea - Stickleback, Gasterosteus spinachia, sexual 

 differences of colour and structure have not been emphasised 

 in descriptions, but the male has the peculiarity of binding 

 together the weeds of which his nest consists by means of a 

 whitish thread spun from his own body. It has been 

 recently proved that this thread is secreted by the kidneys, 

 and is only produced in the breeding season. It must be 

 admitted that it is difficult to indicate any special stimulation 

 that could have caused the kidneys to secrete a tenacious 

 thread in the male only. Yet it is most probable that the use 

 of this thread for securing the nest arose quite unconsciously 

 on the part of the fish. If he were swimming about the nest 

 to arrange it, and a tenacious secretion escaped from his 

 kidneys, it would necessarily become a binding thread. All 

 we have to explain, therefore, is the apparently abnormal and 

 unique secretion. According to Prof. Mobius, as quoted by 

 Greddes and Thomson, the enlargement of the testes, produc- 

 ing a mechanical pressure upon the kidneys, is the cause of 

 the secretion. The pressure, if this view is correct, sets up a 

 pathological condition or inflammation in the kidneys, which 

 results in the secretion of a mucous product, and a somewhat 

 similar product is formed in certain diseases of the kidneys 

 in the human subject. 



Labridce. Among the British species of the family Labridse, 

 sexual dimorphism is most strongly marked in Zabrus mixtus, 

 Fries and Ekstrom. The difference between the male and 

 female appears to be confined to the coloration. The male has a 

 gorgeous appearance, being clothed in bright orange, red, and 

 blue, like some of the saints in pictures by the old masters. 

 The red colour is on the back and sides. Five or six bands 

 of blue radiate backwards from the eye, one being generally 

 continued along the body, below the lateral line to the caudal 



