iv. 1 6 



REPRODUCTION OF LAMPREYS 



"3 



undergo rapid contortions, the eggs being squeezed into the water, 

 while sperms are ejected through the 'penis' (Fig. 75). Fertilization 

 is therefore external, but the sperms must be placed very close to the 



Fig. 75. Spawning lampreys seen in their nest. 

 (After Gage.) 



eggs, for they remain active only for about one minute after entering 

 the fresh water, which provides the stimulus that activates them. The 

 eggs and sperms are not all laid at once; mating is repeated several 

 times until all the products have been shed, after which the animals 

 are exhausted and soon die. The movements of the animals stir up 

 the sand in the nest (this is probably the function of the anal fin of 

 the female) ensuring that the eggs are covered up as they are carried 

 away by the current. 



