406 Studies in the Theory of Descent. 



pupa and imago are variable, and the caterpillar 

 remarkably constant, this likewise being the case 

 with the local form Bryonia, which, according to my 

 theory, is to be regarded as the parent form of 

 Napi (See Part I. of the present volume). 



(4.) There are species which are constant in 

 two stages, and variable only in the third. Thus, 

 a few species can be found in which the larva and 

 pupa are constant and the imago variable. This 

 is the case with Saturnia Yamamai, the imago of 

 which is well known to present numberless shades 

 of colour, varying from light yellow to greyish 

 black, whilst the green caterpillar shows only 

 slight individual differences of marking, and 

 scarcely any differences of colour. The pupa of 

 this species is quite constant. Arctia Caja and 

 Hebe, and CJielonia Plantaginis belong to this 

 same category. 



There are a very large number of species which 

 possess very constant imagines and pupae, but 

 extremely variable larvae. The following are the 

 cases known to me : Macroglossa Stellatarum, 

 Fuciformis and Bombyliformis ; Chcerocampa 

 Elpenor^ Celerio, and Nerii ; Deilephila Galii, 

 Livornica, Hlibn., Hippophdes, Vesper tilio, and 

 Zygophylli; Sphinx Convolvuli ; Acherontia Atro- 

 pos ; Smerinthus Ocellatus and Tilice ; Callimorpha 

 Hera ; Cuculiia Verbasci and Scrophularia. 



Cases in which the variability depends entirely 

 upon the pupa, while the larva and imago are 



