PARTS OF ANIMALS, IV. viii. 



Maiae ** (whose legs are thin) and the crabs called 

 Heracleotic (Avhose legs are short). 



The little tiny crabs, which are found among the 

 catch Avith small fishes, have their hindmost feet flat, 

 like fins or oars, to make them useful for SAvimming. 



The Carides diifer from the Carcinoids in having a 

 tail, and from the Caraboids just mentioned in not 

 having claws. Claws are absent because they have 

 more feet : the material for their growth has gone 

 into the feet. And they have more feet because they 

 swim about more or move about more. 



As for the parts on the under '' surface around the 

 head, in some animals these are formed like gills so as 

 to let in the water and to discharge it ; the lower 

 parts, however, of female crabs are flatter in formation 

 than those of male ones, and also the appendages on 

 the flap are hairier. This is because they deposit 

 their eggs there instead of getting rid of them, as the 

 fishes and the other oviparous animals do. These 

 appendages are wider and larger and so can provide 

 more space for the eggs. In all the Carabi and in 

 all the Carcini the right claw is bigger and stronger 

 than the left. This is because all animals in their 

 activities naturally use the right side more ; and 

 Nature ahvays assigns an instrument, either ex- 

 clusively or in a better form, to those that can use it. 

 This holds good for tusks, teeth, horns, spurs and all 

 such parts which serve animals for assistance and 

 oiFence. 



In Lobsters only, whether male or female, it is 

 a matter of chance which claw is the bigger. The 



" Probably the spiny spider-crab. 

 ' That is, ventral. 



353 



