42 Annals Entomological Society of America [Vol. IX, 



of the somites indicated by the cardica ostia, arteries, tracheae 

 and legs, but this does not prove the double nature of the 

 somites in insects. Embryologists in general, seem to have 

 never found two pairs of tracheal invaginations in any one seg- 

 ment in insects. Patten's second pair of tracheal invaginations 

 in Acilius has proved to be a mass of cells, easily mistaken for 

 tracheal invaginations. Monsters with double appendages 

 occur throughout the animal kingdom very frequently and are 

 generally considered as abnormalities; not as a reversion to 

 primitive types or conditions. 



Lowne, '90, favors the compound segment theory of Patten, 

 but thinks that it has not been sufficiently proved. 



Banks, '93, in studying the chilopods observed a coalescence 

 of the thoracic segments, less apparent in the lower forms 

 (Geophilus) than in the higher ones {Scutigera) and from this 

 concluded that the thorax of insects is composed of five seg- 

 ments, the first, third and fifth bearing legs, the second and 

 fourth bearing wings. He points out in support of this theory 

 that Machilis has a pair of small rudimentary appendages on 

 each abdominal segment, which are also found on the meso- 

 and metathorax in addition to the legs. From this, he argues, 

 that the rudimentary appendages represent legs and hence, that 

 the meso- and metathorax are compound segments. 



These rudimentary appendages found in Machilis occur in 

 other insects, also in Myriopoda and are the so-called styli — not 

 vestigial legs. Jourdain, '88, considered these styli as homol- 

 ogous with the exopodite of Crustacea. Haase, '89, regarded 

 them as modified setce. Henneguy, '04, homologizes the styli 

 with the epipodite of the crustacean leg and Verhoeff, '04, com- 

 pares them to the coxal organs of Myriopoda. At present, how- 

 ever, it is not known exactly what the styli are, but they cer- 

 tainly are not regarded as vestigial legs by modern investigators. 

 Banks' theory has no embryological support and furthermore, 

 what occurs in chilopods is not necessarily any criterion of what 

 occurs in insects. 



Kolbe, '93, considers that the thorax is composed of three 

 primary segments between which, he finds marked off, other 

 "complementary segments," in such forms as the larvae of 

 Lampyris and Raphidia, also in Locusta, Oedipoda, etc. His 

 conclusions are based principally on the larvas of Lampyris and 



