MOUTII-rAltTS OF THE PAL^EMONID PRAWNS. 



47 



the manipulation of food, and for respiration, In all recent 

 Crustacea, however, the specialization of certain of the limbs for 

 each of these functions, and for a fourth, contact with large 

 bodies, such as prey, or the substratum, has caused them to 



Text-figure 20. 



Text -figure 21. 



Text -fig. 20. Maxillule of Calanus sp. 

 „ 21. Maxillule of Cypris sp. 



For lettering see p. 71. 



depart in various directions from the type. Those which were 

 specially adapted for swimming became biramous *, those for 



* This change must have taken place more than once. It is already established, 

 for instance, in the antennae and larval mandibles of various Branchiopoda, which 

 show no trace of it in their other limbs, and it is well developed upon the abdomen 

 of the Nebalia, while it is still but incipient in the thorax. The Conchostraca 

 (text-fig. 5), whose trunk-limbs are almost biramous, show how easily that condition 

 can arise by an alteration in the proportions of the parts of the limb. 



