8 PROCEEDINGS OF THE ACADEMY OF [Jan., 



Japyx, etc., between each chief segment and its corresponding " Vorder- 

 segment," and also in front of each Vordersegment, are found certain 

 minute sclerites which Verhoeff interprets as the remains of two 

 "intercalary" segments. Under these conditions, each of the three 

 commonly accepted thoracic regions would in reality be composed of 

 four subsegments (i.e., a chief and a complementary segment, each with 

 its corresponding intercalary segment), thus giving a total of twelve 

 subsegments for the thorax as a whole. 



In this connection it may be remarked that Banks, '04, is entirely 

 incorrect in stating that his theory is supported by the views of Ver- 

 hoeff. In reality the two are not at all alike, for, while Banks con- 

 siders that the epimeron and episternum represent two annuli, Verhoeff 

 expressly states that these two sclerites are parts of one and the same 

 segment, in front of which he finds the additional so-called comple- 

 mentary and intercalary segments. 



If then, with Banks, we consider the epimeron and episternum as 

 representing two subsegments, a combination of Banks' and Verhoeff' s 

 theories would give five subsegments in each thoracic region, or a total 

 of fifteen for the entire thorax. On the other hand, if MacLeay's, '30, 

 contention, that the prsescutum, scutum, scutellum and postscutellum 

 represent four annuli, be correct, a combination of this with Verhoeff 's 

 theory would raise the total number of thoracic subsegments to twenty- 

 one. This reductio ad absurdum only serves to show to what extremes 

 it may lead if we regard each of the sclerites which chance to be serially 

 arranged as the remains of a vestigial segment. Then, too, in view 

 of the marked tendency toward the formation of separate chitinous 

 plates which, as will be later discussed, takes place largely through 

 mechanical causes, and for the most part without reference to any 

 segmental arrangement, one cannot be too cautious in attributing to 

 them a segmental value. 



While it must be admitted that the "compound-segment" theory 

 is a most attractive and not wholly groundless one, the following 

 serious objections to the above cited theories may be made. Thus, 

 the mere occurrence of four regions in the tergum, or the fact that the 

 pleuron is divided into epimeron and episternum, is not sufficient proof 

 that the segment is compound, since such divisions frequently occur 

 from purely mechanical causes, and wholly without reference to any 

 segmental arrangement — as, for example, the division of each segment 

 into tergum, pleura and sternum. 



Again, one should not lay too great stress upon the conditions found 

 in Myriopoda as an indication of what has occurred in Insecta. A 



