124 





CYCLIC CHANGES 



IV 



¥,*\ 



Fig. Si. 

 Bitterling pair near a mussel. 



Fig. 82. 

 Female bitterling in oviposition. 



continually chased away. Not only are males of the same species driven 

 off, but all sorts of other fishes as well, even females with long ovipos- 

 itors. Those female bitterlings, however, which, apart from possessing a 

 long ovipositor, also adopt a certain posture, namely with the head 

 inclining slightly downwards (inclination-position) appear to attract the 

 special attention of the male. These females do not take flight as the male 

 rushes at them impetuously, but rather convey the impression of being 

 apathetic. When a male comes in the neighbourhood of such a female its 

 behaviour suddenly changes. Displaying himself, and trembling all over, 

 he slowly swims before the female in the direction of the mussel. The 

 female seems fascinated by these tremblings, and follows slowly until it 

 comes near to the mussel. There it inspects the filaments of the exhalant 

 siphon, and in the most favourable case places itself with its tail above 

 the siphon of the mussel, its head slightly downwards, and with a sudden 

 forward movement shoots its ovipositor into the opening. During this 

 manoeuvre, which lasts only a fraction of a second, the displaying male 

 performs extremely rapid trembling movements, which probably con- 

 stitute the actual ovulation stimulus to the female. As soon as the female 

 has deposited her egg and swims away the male, shining in brillant 

 colouring, discharges his sperm from above into the same opening. 



