( CXV ) 



Sucli correspondence has not been observed in any other 

 LepidopterovTS insect. 



If we take into account the fact that Zonosoma {Efhyra) is a 

 characteristic Geometrid genus, although its method of pupal 

 suspension is unique in a family whose species make cocoons 

 or bury, we may feel confident that it has been descended from 

 cocoon-making ancestors, and that Eugonia quercinaria and 

 Urojiteryx scmibucaria give us a clear idea of the steps by 

 which the reduction was effected. 



T/ie effect of Gravity upon the shape of suspended pupse such 

 as those of the JSfympJialinx. — Every naturalist who has 

 watched the pupation of a Vanessid must have observed 

 the extraordinary mobility of the abdominal region of the 

 freshly-exposed chrysalis. Movements of remarkable ampli- 

 tude take place in every direction, and especially in the 

 dorso-ventral plane, these latter being essential for the with- 

 drawal of the posterior segments from the larval skin and 

 the remarkable feat of attachment to the silken boss close to 

 the point from which the skin itself is hanging. Success is 

 only rendered possible by the remarkable contractile power 

 of the intersegmental muscles along the median ventral area. 

 These, by their contraction, keep the rigid hook-armed apex 

 of the abdomen firmly pressed to the outside of the larval 

 skin up which it is being forced, and enable it to press down 

 or push aside any of the stiff spines which oppose the move- 

 ment : these finally bring it to the small silken boss which 

 alone provides a secure basis of attachment for the terminal 

 hooks. For this purpose the ventral muscles require to be 

 far stronger than those of any other region, and we invariably 

 find that they entirely overbalance the dorsal intersegmental 

 muscles in pupae which have been produced on the floor of 

 the breeding-cage. In such pupse the abdominal segments 

 are curved round towards the ventral side, so that the long 

 axis of the apical part forms at least a right angle with that 

 of the thoracic region, and this attitude becomes stereotyped 

 with the hardening of the pupal cuticle and the consequent 

 loss of all power of dorso-ventral movement. These free 

 pupae form a striking contrast with the normal attached 

 individuals in which the long axis of the abdominal segments 



