416 



TEXT -BOOK OF ZOOLOGY 



Besides, the animal is compelled to hold fast its prey, which otherwise 

 would soon be washed away, especially in running water. 



2. Accordingly, the 

 crayfish must be pro- 

 vided with organs for 

 holding and dividing 

 its prey. Such organs 

 are the large pincers 

 or claws of the first pair 

 of thoracic legs (see 

 Section vi.), which, on 

 account of their great 

 strength, serve also as 

 prehensile and defen- 

 sive organs. They are 

 formed on the general 

 plan of shears, viz., by 

 the last joint of the 

 limb being movably 



Kf.2. opposed against a pro- 

 longation of the penul- 

 timate joint. These 

 pincers cannot, how- 

 ever, be brought in 

 contact with the mouth 

 (show this by trial), 

 which is effected by 



3. The much smaller 

 pincers of the two suc- 

 ceeding pairs of limbs, 

 by means of which the 

 detached portions of 

 food are conveyed to 



4. The mouth parts. 

 Of these there are six 

 pairs. The foremost, 

 called the mandibles, 

 consists of a hard- 

 toothed, masticatory 

 portion, which is seen 



at a glance to be the principal instrument for dividing up the food. 

 (Compare with mandibles of insects possessed of masticatory mouth 



Tex Fikst Limbs op Oeayfish, Eight Side 

 Below). (Slightly enlarged.) 



F.l. and F.2., Antennules and antennse ; Ok 



Uk.l. and Uk.2., first and second maxillffl ; Kf.l., Kf.2.. 

 and Kf.3., first, second, and third maxillipedes ; Bf.l. and 

 Bf.2., first and second ambulatory legs ; K., branchise. 



(SEEN FROM 



mandibles 



