MOITTJI-PARTS OF THE PAL^EMONID PKAWXS'. 



47 



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

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

 each of these functions, and for a fourth, contact with lai-ge 

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



Text-fis?ure 20. 



Text-figure 21. 



Test-fig. 20. Maxillule of Calauns 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 establishedj 

 for instance, in the antennaB 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 Nehalia, while it is still but incipient in the thorax. The Conchostraca 

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

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



