24 



Outline of Life-history 



B 



instance, have red blood, others not ; some have blood- 

 gills on the eleventh segment, which are wanting in 

 others. Some pupae have prothoracic respiratory trum- 

 pets ; others have branched 

 tracheal gills instead. This 

 adaptive specialization of 

 particular stages is no new 

 thing in zoology. Natural 

 selection seems to act upon 

 the separate stages of certain 

 life-histories almost as it acts 

 upon species. 



Baron Osten Sacken ^ 

 quotes two cases of Nemocera 

 in which the reverse relation 

 obtains, that is, the larvae 

 are closely similar, but the 



Fi«. u— Papa of Corethra. A, ^168 SO UnlilvC aS tO bo re- 

 ventral view. B, side view To show ferred to different families, 

 the prothoracic respiratory trumpets. 



(From MiaU's Natural 'llidoru of rj^]^Q j^^q caSCS are (ci) MvCC- 

 Aquatic Insects.) ^ ' ^ 



tobia and Rhyphus, (6) Ano- 

 pheles and Dixa. We are unacquainted with the early 

 stages of Rhyphus, and will therefore offer no remarks 

 on case a. The larvae of Anopheles and Dixa, though 

 so like as to have deceived one experienced entomologist, 

 are not, we think, so like as to raise any new biological 

 question. They are easily and certainly distinguished 

 by an attentive observer, and many definite points of 

 difference could be brought forward. They are only 

 superficially alike, and the resemblance is merely 

 adaptive, like the resemblance of some Isopod Crustacea 

 to Millipedes^. 



* 1892, pp. 418, 465. 



2 It has been remarked that larvae of Noctuae (e. g. Agrotis), thoiigli 

 almost exactly alike, may produce moths of very different appearance. 



