SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 25 1 



linked to the above by one of those profound physiological 

 unities which show how superficial after all are the utmost 

 contrasts of organic form, — we refer to the viscid threads with 

 which the male stickleback weaves his nest. Mobius has 

 shown that the kidneys are greatly affected by the mature 

 testes ; that they produce, by a now^ normal ]mthological pro- 

 cess, special waste or katabolic elements, in the form of mucous 

 threads. The male gets rid of this uneasy encumbrance (which 

 has a somewhat parallel pathological equivalent in higher ani- 

 mals), by rubbing itself against objects, and thus almost 

 mechanically has been evolved the familiar weaving of the 

 aquatic nest. 





The Nest of the Stickleback (Gastcrosteiis). — From Thomas Bolton. 



§ 8. Incubation. — The physiological sacrifice of the female 

 birds does not end with providing the large capital of nutritive 

 material with which the germ is endowed, but is continued in 

 all the patience of brooding. In passerine birds the male 

 relieves the female in her task of love, and in the ostrich tribe 

 takes the duty usually upon himself. In the cuckoos and cow- 

 birds the parental care is shirked, and with varying degrees of 

 deliberateness the eggs are foisted into foster nests, and the 

 young thus put out to nurse. After the fatigue of reproduction 

 it is perhaps natural enough that the female should rest awhile 

 upon the eggs in the shelter of the nest, and since there is 

 observed to be an increased circulation in the skin of the 



