I04 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.97 



that can be taken concerning the homologies of the ganglionic rudi- 

 ments, since it disposes of the latter in a manner entirely consistent 

 with the evident facts in other arthropods. According to Silvestri the 

 ganglia of the antennae (AntGng) are neural masses situated mesad 

 of the antennal bases, and the first pair of postoral ganglia (TcrGng) 

 are the tritocerebral ganglia (ganglia of the intercalary somite). It 

 should be observed that the antennal ganglia, as shown by Silvestri, 

 have a preoral position and are not separated from the protocerebral 

 lobes of the brain (Per). 



Among the higher arthropods the more primitive stages in the brain 

 development are generally not shown in embryonic recapitulation, for 

 the proto-deutocerebral centers are usually proliferated from the ecto- 

 derm as a unified ganglionic cell mass, just as in the Onychophora 

 and in many of the Annelida. It is observed by Baden (1936) and 

 by Roonwal (1937), however, that the brain of the grasshopper 

 (Melanoplus, Locusta) is formed from five pairs of ganglionic 

 centers, three of which give rise to the protocerebrum and the optic 

 lobes, and the other two to the deutocerebrum and the tritocerebrum, 

 respectively. On the other hand, Nelson (191 5) finds that in the 

 honey bee the lateral surfaces of the primarily undivided cephalic 

 lobes of the embryo become directly differentiated into three areas 

 from which are proliferated the neural centers of the protocerebrum, 

 the deutocerebrum, and the tritocerebrum. 



In view of the well-authenticated examples of a diffuse origin of 

 the cerebral ganglionic centers in the arthropods, the theory of 

 Holmgren (1916) and of Hanstrom (1928) that the protocerebrum 

 and the deutocerebrum are secondarily differentiated parts of a primi- 

 tive, undivided archicerebrum does not appear to be substantiated by 

 the facts of embryogeny. However, since the definitive brain is 

 evidently a conglomerate of primitively separate ganglionic centers 

 in the Annelida as well as in the Arthropoda, the general contention 

 of these authors is not invalidated, namely, that both the protocerebral 

 and the deutocerebral parts of the arthropod brain belong to the 

 preoral prostomial region of the head, and, therefore, together 

 represent the annelid archicerebrum. 



The concept that all coelomic sacs and corresponding nerve centers 

 represent postoral somites seemed reasonable enough, as applied to 

 the arthropod head, when only antennal sacs were known; it was 

 somewhat stretched, though still acceptable, when preantennal sacs 

 were discovered ; but now that we must add a third pair of cephalic 

 sacs lying directly before the mouth in the labral region it begins to 

 look farfetched. The theory here proposed, illustrated at D of 



