

The Crayfish 75 



claws and feelers, keeping careful watch on the 

 passers-by. Larvae of insects and tadpoles, small 

 frogs, and other objects which come within the 

 animal's reach are seized and devoured. In the 

 spring of the year female crayfish are found to 

 be laden with eggs attached to their tails ; when 

 hatched they give rise to minute young beings 

 which are sometimes seen hanging on their 

 parent's body, under whose protection they 

 spend the first few days of their existence. 



Scattered over the surface of the body of a 

 crayfish there are a multitude of tactile sensory 

 organs, known technically as setae : they are 

 particularly well developed on the animal's 

 antennules or feelers. The setae arise from 

 cells of the ectoderm, and at their attached sur- 

 face receive terminal fibres which originate in 

 the nerve cells of the animal's mid-brain. On 

 the under side of the outer branch of the anten- 

 nule sensory structures exist, which there is 

 reason to think form part of an olfactory ap- 

 paratus. The eyes of a crayfish consist of 

 highly complex structures, arranged so as to 

 bring waves of light to bear upon the fore ends 

 of two bundles of optic nerve fibres; thus 



