REPRODUCTION 



267 



The full growth of the ovipositor and preparation of the female for 

 spawning depends on the presence in the water of the male and also 

 of the swan mussel. Water in which males have been kept stimulates 

 growth of the ovipositor. When the female is ready to deposit the eggs 

 she adopts a vertical position in the water and the spawning male, in 



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Fig. 160. Male and female bitterling (Rhodeits) with swan mussel 

 in which eggs are about to be deposited. (From Norman.) 



full nuptial coloration, swims around her. An egg passes into the 

 oviduct and erection of the ovipositor is produced by pressure of the 

 urine, produced by contraction of the walls of the urinary bladder, the 

 exit being blocked by the egg. The extended ovipositor is thus able 

 to place the egg within the siphon of the mussel and the male then 

 immediately thereafter sheds his sperms over the opening and they 

 are presumably carried in by the current. The whole process shows 

 the elaborate interplay of internal devices and external stimuli neces- 

 sary for the perfection of this remarkable method of caring for the 

 young. Yet the various features are all developments of systems found 

 in other vertebrates. 



