54 



MR. L. A. BORRADAILE ON THE 



disappeared, either by fusion with the trunk or with the second 

 joint, or perhaps sometimes by excalation. 



The fifth endite and those distal to it belong to that part of the 

 limb which stands beyond the attachment of the flabellum, and 

 represent the endopodite of the biramous limb. The maxillae of 

 Cerataspis and larval Natantia (text-figs. 15-18) seem to show 

 that each of these endites is borne upon a portion of the limb 

 which represents a single joint of the biramous appendage, and 

 that the apical lobe is an unsegmented distal region of varying 

 extent, corresponding to the dactylopodite and any adjacent 

 segment or segments not represented by an endite. 



Text-figure 28. 



Guathobase of thoracic limb of Lepidurus sp 



It is fair to assume that all these relations existed in the 

 primitive crustacean appendage, and that the latter gave rise to 

 the biramous limbs by a transformation in which the axis of the 

 limb became jointed in the way indicated, the endites in great part 

 or altogether disappeared, and the flabellum approximated in shape 

 to the distal part of the axis and came to stand side by side with 

 it at the end of the third (or, if the precoxa were not separate, 

 the second) joint of the limb. 



8. With the original phyllopod limb, thus reconstructed, the 

 jaws of Malacostraca may be compared as follows :- — In the 



