792 On the Homologies of the Crustacean Limb. [October, 



come down to us by a different branch of the Crustacean ances- 

 tral tree, and have arisen entirely independently of the Phyllo- 

 podous branch, by a line leading back directly to the ancestral 

 Nauplius, the common ancestor of all the Neocarida. 



Nor does it seem to us that this statement or hypothesis is 

 weakened when we consider the resemblances between the tho- 

 racic feet of the Phyllopods and the maxillae and maxillipedes of 

 the Decapoda. When we compare the leg of a Phyllopod with 

 the second maxilla 1 of the lobster (Fig. 

 6, B) or crayfish, we can detect a close 

 homology, the chief difference being in 

 the fact that the lobes of the' endopodite 

 are less numerous in the Decapod than 

 in the Phyllopod. Tl 

 blance is based on the fact, which ap- Fig. 5.— Mandible of the 

 pears to have been overlooked by Claus^ t £\ p ^ w * m ' ameruanus: 

 and Lankester, i. e., that as in the Phyl- 



lopodous limb, the maxillae of the Decapods have no jointed 

 axis, the limb consisting of epipodal and endopodal portions 

 alone, the stem or axis being wanted. In the maxillipedes, 

 where part of the endopodal region of the limbs becomes, as 



f lh;. :;■ ..,,..■ 



pod limb.) 



Lankester claims, two multiarticulate endites, the fifth and sixth ; 

 or, as in the thoracic leg, becomes a single seven-jointed endite, 

 the homologies cannot with certainty be traced. The lobster s 

 thoracic leg consists of the jointed axis which is the homologue 

 of perhaps the fifth endite of the Phyllopodous foot (Lankester), 



1 The resemblance to the second maxiihe of the young lobster in its first stage 

 when freshly hatched, is still more striking. See Smith's Early stages of the Amer- 

 can Lobster, PI. xrr, Fig. 4. 



