INSECT SPINASTERNAL MUSCULATURE — CHADWICK 



149 



todea, Grylloblattodea, Orthoptera, Psocoptera, and Plecoptera. The 

 Dermaptera also are possibly orthopteroid ; but in any case they have 

 probably had a long independent existence. 



4. The neuropteroid series includes the Megaloptera, Coleoptera, 

 and Neuroptera, and probably the Trichoptera and Lepidoptera. If 

 the Mecoptera belong here, they were separated from the other orders 

 named at an early date. 



5. The relationships of the Hymenoptera are quite uncertain. 



THYSANURA- 



^ 



__jC 



<, 



^^-^ORTHOPTERA 

 PSOCOPTERA ISOPTERA 



s. 



BLATTARIAE 



■NT y 



"^^GRYLLO- f 

 BLATTODEA 



MANTODEA 



y 



^PLECOPTERA deRMAPTERA>' 



ODONATA 



y 



^MEGALOPTERA 



MECOPTERA 



y 



\ 



COLEOPTERA 



NEUROPTERA 



"-TRICHOPTERA 

 ^LEPIDOPTERA 



Fig. I. — The apparent relationships of some orders of insects, as seen in their 

 spinasternal musculature. Uncertain affinities, for which there is some evidence, 

 are indicated by question marks. Available data do not permit even tentative 

 placement of the Mallophaga, Phasmatodea, Embiodea, Ephemeroptera, Thy- 

 sanoptera, and Homoptera, which are known to possess a few spinasternal 

 muscles, 



6. The Odonata have been separated from the other Pterygota for 

 a very long time. Their spinasternal musculature indicates an early 

 derivation for them, but does not permit a choice among several 

 possibilities. 



7. Also difficult to place are the Mallophaga and Phasmatodea. 

 Conventional derivations for these two orders appear to conflict with 

 the facts revealed in their spinasternal musculature, but the latter 

 is too reduced to serve as a guide to definite placement. 



8. The spinasternal muscles of the remaining orders that have been 

 studied are not informative as to the affinities of these groups. These 

 include the Embiodea, Ephemeroptera, Thysanoptera, Homoptera, 



