SECT. Ill 



THE APPENDAGES 



37 



cirrus forming the exopoditc. As the larva grows, 

 the endopodite gradually degenerates, leaving the 

 sensory cirrus to form the distal end of the limb 

 which is thus a sensory organ (compare also Figs. 

 34 and 35). 



III. TJie jMandiblcs.—T\\Q.?,c are the first limbs which 

 admit of undoubted comparison with parapodia. We 

 find, however, that while the dorsal branch has entirely 



Fig. Z.—A, diagram of mandible; j, shell-fold. At d the dorsal parapodium has 

 disappeared, but is indicated by the musculature, v, ventral parapodium lorm- 

 ino- the mandible itself, the musculature coming from the sternal plate (j/). h, 

 diagram of ist maxilla. At d, a larger rudiment of the dorsal parapodium is 

 retained than in the mandible. 



disappeared, the ventral has grown enormously in all 

 directions to form the powerful masticatory limbs 

 which are such a striking feature in the Apodidae. 

 That these mandibles are homologous with the gnatho- 

 bases of the trunk limbs, and therefore, according to 

 our view, with the ventral parapodia of the Annelida, 

 may be seen at once by comparing their musrcles with 



