PkyUtti Parallelism in Afctanwrp/iic Species. 483 



unite them with these into one group. The two 

 certainly differ in certain details of structure in the 

 mouth-organs and in the number of segments, 

 abdominal legs, &c., to a sufficient extent to 

 warrant their being considered as two sub-orders 

 of one larval order; but they would in any case be 

 regarded as much more nearly related in form 

 than the caterpillar- and maggot-like types of the 

 Hymenopterous larvae. 



Is it not conceivable, however, that the imagines 

 of the Hymenoptera that ichneumons and wasps 

 may be only accidentally alike, and that they have 

 in fact arisen from quite distinct ancestral forms, 

 the one having proceeded with the Lepidopterous 

 caterpillars from one root, and the other with the 

 grub-like Dipterous larvae from another root ? 



This is certainly not the case ; the common 

 characters are too deep-seated to allow the suppo- 

 sition that the resemblance is here only superficial. 

 From the structure of the imagines alone the 

 common origin of all the Hymenoptera may be 

 inferred with great probability. This would be 

 raised into a certainty if we could demonstrate 

 the phyletic development of the maggot-formed 

 out of the caterpillar-formed Hymenopterous larvae 

 by means of the ontogeny of the former. From 

 the beautiful investigations of Biitschli on the 

 embryonic development of bees 1 we know that the 



1 Aitsrhrift fiir wissenschaftl. Zoologie, vol. xx. p. 519. 

 I i 2 



