Ill] 



OF DIMORPHIC GROWTH 



215 



variation*. In the "complete metamorphosis" of a beetle there 

 is no room for a moult more or less, and the reason for the two 

 modal sizes remains hidden (Fig. 61). 



But new hght has been thrown on the case of the earwigs, which 

 may help to explain other obscure diversities of shape and size 

 within the class of insects. At metamorphosis, and even in a simple 

 moult, the external organs of an insect may often be seen to unfold, 

 as do, for instance, the wings of a butterfly; they then quickly 

 harden, in a form and of a size with which ordinary gradual growth 



I 



200 



Head of 0.'tauru8;two 

 forms of maJe 



^N 



A. 



0*5 1-0 



Length of horn (mm.) 

 Fig. 61. Two forms of the male, in the beetle Ontkophagvs taurus. 



has had nothing directly to do. This is a very peculiar phenomenon, 

 and marks a singular departure from the usual interdependence of 

 growth and form. When the nymph, or larval earwig, is about to 

 shed its skin for the last time, the tail-forceps, still soft and tender, 

 are folded together and wrapped in a sheath; they need to be 

 distended, or inflated, by a combined pressure of the body-fluid 

 (or haemolymph) and an intake of respiratory air. If all goes well, 



* Rene Paulian, Bull. Soc. Zool. Fr. 1933; also Le polymorpMsme des mMea de 

 Cddoptires, Paris, 1935, p. 8. 



