FISHES 175 



be lit up by an internal fire. The female is recognisable 

 at this time by a long ovipositor, into which it forces an 

 egg or ovum. With this it swims to one of the larger 

 painter's gapers, which stretch out their respiratory and 

 cloaca - opening sluggishly from the sand. The fish 

 drops its ovum into this, and the male, its whole body 

 quivering, pours its seed over it. The mussel tries to 

 get rid of the unwelcome foreign body by violent con- 

 tractions, but does not succeed as a rule. The egg 

 passes into its gill-chamber, and the little creature that 

 develops from it forms a sort of transverse swelling 

 behind its head, with two processes that help it to 

 strengthen its hold. These projections afterwards 

 disappear and the fish abandons the home of its 

 childhood, which had sheltered it completely from 

 danger. 



But the mussel has its revenge for this involuntary 

 shelter. When the hour comes for its reproduction, 

 it thrusts out its brood through the opening. The 

 young mussels fall to the bottom of the water, open 

 the shell, and send out a long thread. This has a 

 sticky surface, and gets entangled with the threads of 

 other young mussels, so as to form a firm and com- 

 plicated net, from which the little animals hang. If 

 a fish it is generally a rhodeus or a perch runs 

 into the net, the mussels come into contact with its 

 body, and immediately bring their shells together, 

 and the sharp edges press deep into its flesh. A 

 growth is formed in the skin of the fish at the injured 

 spot, and at length covers the whole mussel. It then 

 lives at the expense of the fish, though it does not 



