THE EEPEODUCTION OF THE SPECIES. 39 



mentary limb straightens out, and, though very small, 

 acquires all the organization appropriate to that limb. 

 At every moult it grows ; but, it is only after a long time 

 that it acquires nearly the size of its uninjured and older 

 fellow. Hence, it not unfrequently happens, that crayfish 

 are found with pincers and other limbs, which, though 

 alike useful and anatomically complete, are very unequal 

 in size. 



Injuries inflicted while the crayfish are soft after 

 moulting, are apt to produce abnormal growths of the 

 part affected; and these may be perpetuated, and give 

 rise to various monstrosities, in the pincers and in other 

 parts of the body. 



In the reproduction of their kind by means of eggs the 

 co-operation of the males with the females is necessary. 

 On the basal joint of the hindermost pair of legs of the male 

 a small aperture is to be seen (fig. 8, A; vd). In these, the 

 ducts of the apparatus in which the fecundating substance 

 is formed terminate. The fecundating material itself is a 

 thickish fluid, which sets into a white solid after extru- 

 sion. The male deposits this substance on the thorax 

 of the female, between the bases of the hindermost pairs 

 of thoracic limbs. 



The eggs formed in the ovary are conducted to* apertures, 

 which are situated on the bases of the last pair of ambula- 

 tory legs but two, that is, in the hinder of the two pair 

 which are provided with chelate extremities (fig. 3, B ; od). 



