TRANSFORMATIONS OF THE INSECT. 69 



ovate, flattened, with four long seise in front and two behind, 

 with the sides of the body emarginate and spinulated. They 

 were found under logs. "When the larva is full grown, it de- 

 tuches itself from the skin, which retains its form, and within 

 which the insect changes into a white opaque fleshy grub con- 

 sisting apparently of thirteen segments which gradually dimin- 

 ish in size from one end to the other. There are no limb-cases. 

 According to analogy the pupa should be ' incomplete ; ' it is 

 probable, therefore, that the legs and wings make their appear- 

 ance at a later stage. If this be so the perfect form is only 

 attained after passing through three well-marked stages. I re- 

 gret, however, that the specimens at my disposal did not enable 

 me to decide this point." (Trans. Ent. Soc. London, Third 

 Ser. i, 1862.) 



Haliday states that Tlirips goes through a propupa and pupa 

 stage. There are five well-defined stages in the Homopterous 

 Typhlocyba, and more than three in Aphis. Yersin has noticed 

 several stages in the development of Gryllus campestris, and 

 the genus Psocus has four such stages. 



The duration of the different stages varies with the changes 

 of the seasons. Cold and damp weather retards the process of 

 transformation. Re'aumur kept the pupa of a Butterfly two 

 years in an ice-house before, on being removed to a warm place, 

 it changed to a butterfly. Chrysalids survive great alter- 

 nations of heat and cold ; they may be frozen stiff on ice, and 

 then, on being gradually exposed to the heat, thaw out and 

 finish their transformations. 



Retrograde Development. There are certain degradational 

 forms among the lowest members of each group of Insects 

 which imitate the group beneath them. The Tardigrade* (which 

 are considered by some authors to be allied to the Mites) are 

 mimicked by the low parasitic worm-like Demodex folliculorum ; 

 the low Neuroptera, such as Lepisma. imitate the Myriopoda ; 

 and the wingless Lice remind us of the larvae of the Neuropter- 

 ous Hemerobius. 



Among the Coleoptera, the history of Stylops affords a strik- 

 ing example. The active six-footed larva is transformed into 

 the strange bag-like female which takes on the form of a cylin- 

 drical sac, the head and thorax being consolidated into a 



