64 SEX 



on the back. It is formed by an invagination 

 of the skin from behind forwards, and into 

 it the male pushes the eggs with his hind feet. 



Among fishes the sexes are often very like 

 one another, but there are many illustrations 

 of sex-dimorphism. In some gristly fishes 

 or Selachians, like the skate, the males 

 have very conspicuous " claspers." They 

 are specialised parts of the pelvic fin, have 

 a complex musculature and skeleton, and are 

 entirely awanting in the females. In the 

 male Chimsera, these parts are even more 

 complicated, and " on the head there is 

 further a remarkable knobbed and curved 

 spine projecting forwards, and covered at its 

 extremity with sharp denticles. There can be 

 no doubt that this also is used for holding the 

 female, although the exact mode in which it is 

 used has not been observed " (Cunningham). 



The male salmon has the tip of the lower 

 jaw turned up and enlarged at the breeding 

 season. It forms a curious blunt hook-like 

 process, which is possibly of use when the 

 males charge one another. In many cases, 

 such as lumpsucker and stickleback, which 

 are as contrasted types as one can think of, 

 the males are distinguished at the breeding 

 season by the brilliant colouring. In the 

 male sea-horse (see Fig. 12) and some of its 

 relatives, the most striking sex-distinction is 

 the possession of a pouch in which the eggs 

 develop. It is noteworthy that in the genus 

 Solenostoma, the pouch is in the female, which 

 is more vividly coloured and spotted than the 

 male. Perhaps she has to attract her mate 1 



There is among insects an embarrassing 



