EXCRETORY AND REPRODUCTIVE SYSTEMS 351 



Except in the Monotremes, the base of the oviduct in the 

 mammals becomes specialised to form the uterus, in which the 

 embryos undergo development. According as to whether 

 the bases of the two oviducts remain separate or become 

 fused together the uterus may be double or single. 



Another peculiarity of the mammalian reproductive 

 system, is the fact that in the male, the testes usually leave their 

 position in the roof of the abdominal cavity, and descend into 

 scrotal sacs (see p. 150). 



While claspers or copulatory organs are present in the 

 males of several fish, the amphibia lack them (except the 

 Gymnophiona), and fertilisation has to take place in water 

 since the sperm require a fluid medium. In Anura the eggs 

 and sperm are shed together into the water. In the newts, as 

 a rule, the male lays a packet of sperm, and then gives a display 

 of " courtship " in front of the female to stimulate her to 

 pick up the packet with her pelvic limbs and place it in her 

 cloaca. During the breeding season the male has specially 

 developed secondary sexual (epigamic) characters, such as the 

 crest and the colour of the belly, which assist in the courtship 

 activities. 



In the amniotes, fertilisation is internal, and the sperms 

 are introduced into the cloaca of the female by the copulatory 

 organ or penis of the male. In this way, the amniotes are 

 independent of water for fertilisation. 



A feature of considerable interest is the increase in care 

 of the young after they are hatched, by the parents. This 

 increases in the higher groups of vertebrates, and all stages 

 can be found in the evolution of the family, from the condition 

 of Amphioxus where fertilisation takes place in the sea water 

 outside the parents which are in no way concerned with the 

 development of the young, to that of man. This evolution 

 has involved the development and perfection of characters of 

 behaviour as well as those of structure. The first step in this 

 direction is usually the habit of protecting the eggs until the 

 young hatch. In several species of fish, the eggs are laid in 

 holes or in nests specially prepared by the parents, and the 

 male remains on guard. This habit is resorted to by Proto- 



