614 MARGARET ROBINSON. 



I would, therefore, arrange the mouth parts in the four 

 groups thus : 



Hexapoda. Crustacea. Diplopoda. Chilopoda. 



Mandibles, Mandibles. Mandibles. Mandibles. 



Maxillulse (Hansen First maxilla;. Pirst maxillae. Tirst maxillae. 



and Folsom). 



First maxillae. Second maxillse. Gnatliocbilarium. Second maxilla). 



Labium. First maxillipede. Post-maxillary seg- Maxillipede. 



nient. 



In stage B the size of the first maxillge as compared with 

 that of the other appendages is much reduced, and no trace 

 of them can be found in the mouth parts of older larvas. My 

 material was very scanty, and only three series of longitudinal 

 sections through stage B were cut. In each of these series, 

 however, one could see the first maxillte apparently in process 

 of fusion with the mandible. Perhaps it would be better to 

 say that one could see it being absorbed by the mandible 

 (fig. 4). And just as one could see the apparent absorption 

 of this maxillula by the mandible, so also could one see the 

 absorption of its ganglion by the mandibular ganglion (tig. 5). 

 Provided that any fusion of ganglia or appendages takes place 

 the above is the manner in which one would expect it to do 

 so. For the tritocerebral rudiments undoubtedly join the 

 deuterocerebrum which lies in front of them, and not the 

 mandibular ganglion which lies behind them, and the 

 general tendency of fusion in the Arthropoda is from 

 behind forwards. 



If, as I believe, tliese maxillulae fuse with or become part 

 of the mandibles, they can hardly be homologous with 

 the maxillulce found by Carpenter (1905) in the adult 

 Polyxenus, for the inferences which lie draws from his 

 observations on the mouth parts of that Diplopod would lead 

 one to suppose that the maxillula) there had fused with the 

 maxillae during the growth of the gnathochilarium. 



This matter certainly requires further investigation, though 

 it seems, for reasons which are given below, extremely 



