Phylclic Parallelism in Aletamorp/u'c Species. 485 



differing somewhat from those of the other seg- 

 ments ; that is to say, they have descended from 

 larvae which possessed a structure generally 

 similar to that of the existing saw-fly larvae. The 

 common derivation of all the Hymenoptera from 

 one source is thus established with certainty. 4 



But upon what does this great inequality in the 

 form-relationship of the larvae and imagines de- 

 pend ? The existing maggot-like grubs are with- 

 out doubt much further removed from the active 

 caterpillar-like larvae than are the saw-flies from 

 the Aculeate Hymenoptera. Whilst these two 

 groups differ only through various modifications 

 of the typical parts (limbs, &c.), their larvae are 

 separable by much deeper-seated distinctions ; 



4 [The grub-formed Hymenopterous larvae, like the larvae 

 of all other holometabolous insects, thus represent an acquired 

 degenerative stage in the development, /. e. an adaptation to 

 the conditions of life at that stage. Bearing in mind the 

 above-quoted observations of Biitschli and the caterpillar-like 

 form of the Terebrantiate group of Hymenopterous larvae, the 

 following remarks of Balfour's (Joe. (it. p. 353), appear highly 

 suggestive : " While in a general way it is clear that the 

 larval forms of insects cannot be expected to throw much light 

 on the nature of insect ancestors, it dots nevertheless appear 

 to me probable that such forms as the caterpillars of the I^pi- 

 doptera are not without a meaning in this respect. It is easy 

 to conceive that even a secondary larval form may have been 

 produced by the prolongation of one of the embryonic stages ; 

 and the general similarity of a caterpillar to Peripatus, and the 

 retention by it of post-thoracic appendages, are facts which ap- 

 pear to favour this view of the origin of the caterpillar form." 

 so Sir John Lubbock, he. fif., pp. 93 and 95. R.M.] 



