520 PROCEEDIXaS OF THE NATIOXAL Mlh'^EUM. vol. xxxvi. 



SCOLOPENDRID.T^r 



Head. 



Maxillipod segment. 

 First leg-l»earing segment. 



Intercalary segment. 

 Second leg-bearing segment. 



Intercalary segment. 

 Tliird leg-bearing segment. 



Intercalary segment. 

 Fourth leg-bearing segment. 



Intercalary segment. 

 Fifth leg-bearing segment. 



Intercalary segment. 



JAPYGlD.li:. 



Head. 



Microthorax. 



I'rothorax. 



Presternal plnlcs ( vdrplatten). 

 Stenothorax. 



Small intercalary ring. 

 ^lesothorax. 



Presternal iilatcs ( vorplattenl. 

 Cryptothorax. 



Small intercalary ring. 

 Metathorax. 



Presternal plates ( vorplatten). 



Thus, it is supposed that tico pairs of Scolopendrid segments — a 

 leg-bearing and an intercalary segment in each pair — have been re- 

 duced to one seg7nent in ordinary insects. This reduction has re- 

 sulted not from a combination of .segments but from a suppression 

 first of the intercalary segments of the chilopod and then of the 

 alternate remaining leg segments. The intercalary segments of 

 Scolopendrida\ in other words, are not the small segments of J apij.v^ 

 but are the much more rudimentary traces of segments between these 

 and the large segments. Verhoeff's own statement (1903c) is as 

 follows : 



The intermediate segments (zwiscben-segmente) of insects are reduced ])ri- 

 mary segments, inherited from Chilopodan ancestors and which liave united 

 into a double segment with the large primary segment inun(Mliately Itebind. 

 while the intercalary segment of the original double segment of the rhiloixxls 

 has become almost entirely extinct. 



According to this theory, then, the primitive thorax consisted of 

 ten segments. However, all but three of these have been eliminated 

 in all but the very lowest insects, ajid the eliminated segments have 

 taken no part in the formation of the plates of the body wall in pres- 

 ent-day insects. It is certainly no difficult matter to show that the 

 sclerites are formed during postembryonic growth and are purely 

 secondary divisions of the body wall of one segment. Hence, this 

 theory of Verhoeifs is entirely tenable, since it deals only with condi- 

 tions which are presumed to be obliterated before the thoracic plates 

 begin to form. 



However, it must be admitted that all this elaborate scheme is 

 based on an excessive use of the imagination. No proof is adduced 

 to shoAv that the intermediate and intercalary sclerites of Japyx are 

 not secondarily developed plates or even subdivisions of the prin- 

 cipal segments. Desguin (1008), in reviewing this notion of the 

 multiple nature of the thorax in A]Dtera, concludes that neither the 

 anatomical nor the embryological evidence is sufficient to prove 

 whether these intermediate sclerites represent true segments or not. 

 Borner (1003) also gives a good criticism of some of Verhoeff's ex- 

 travagant theories. 



