158 THE SHORTER SCIENTIFIC PAPERS 



Such a view I earlier presented (1913) in a brief dis- 

 cussion concerning the relationship of the parapodium of 

 the Polychaetes to the various areas of the maxilla and 

 other appendages of the insects. The direct derivation 

 of the insects and their allies from such an ancestral type 

 permits the explanation of many characters not easily 

 accounted for on any other basis. While Mayer (1876) 

 advocated the origin of the insects from an annulate 

 worm, which eventually developed ventral and "pos- 

 sibly" dorsal appendages, the implication was that they 

 were newly developed, no suggestion being made of any 

 correspondence between the parapodia and the appen- 

 dages of the insects. The particular point that Mayer 

 had in mind was in establishing the numerical relationship 

 between the segmental organs of the hypothetical an- 

 nulate worm consisting of eighteen segments which he 

 assumed to be the ancestor of the insects, and the spiracles 

 taken together with the malpighian tubules of the insect. 

 The conclusions formulated in this connection, however, 

 were so severely criticized by Brauer (1878) that, what- 

 ever merit may have existed in the work, it was soon for- 

 gotten, except as the historical "Archentomon theory." 



The body of the typical insect so far as the evidence is 

 available at the present time consists of twenty-two seg- 

 ments, provided one accepts the existence of a post-man- 

 dibular segment bearing the appendages termed the super- 

 linguae. On the basis of the specialization of the seg- 

 ments in groups it has been customary to speak of the 

 cephalic region, the thoracic region and the abdominal 

 region of an insect. In the head region and in the ab- 

 dominal region, however, a secondary grouping of seg- 

 ments has taken place so that one may with propriety 

 state that an insect is a heterometameric organism formed 

 from five homometameric segmental groups. These 

 groups consist of a prestomal area of three segments, a 

 poststomal area of four segments, a thoracic area of three 

 segments, an abdominal area of seven segments and a 

 caudal area of five segments. 



Afforts to arrive at a conclusion as to the structure of 

 a typical segment of the insects acceptable to those inter- 



