xxm 



larva fed by its foster-parent, and with the same food ? The same 

 questions may be applied to Chrysis and Odynerus, Ripiphorus and 

 Vespa, Sitaiis and Anthophora. Some little, but, alas ! very little, 

 light has been thrown on the economy of Stylops, and still less on that 

 of Meloe, the food and growth of which in its active hexapodal state 

 is yet unknown to us. 



What a vast field of conjecture is opened up by the discovery of 

 isomyious pairs ! What is the teaching of this phenomenon ? How 

 is it that beings beginning life with such exceeding difference, should 

 approach so nearly in their ultimate state, that they are scarcely 

 to be distinguished from each other ? The familiar instance of the two 

 Acronyctas, Psi and tridens, first called my attention to this. It is 

 now made manifest by a hundred examples; the most recent are 

 those of Lophyrus rufus and L. similis, worked out by Vollenhoven, 

 and Eupithecia fraxinata and E. innotata, discovered by Mr. Crewe. 

 Whither does this discovery tend, and in what does it differ from Mr. 

 Darwin's dimorphism ? Are the isomyious pairs really distinct, and 

 are the dimorphous pairs really identical as species ? We know it is 

 asserted that a cowslip may produce a primrose, and that primrose a 

 cowslip, and so on throughout countless generations. In like manner 

 Volucella plumata may produce Volucella bombylans, and Volucella 

 bombylans, Volucella plumata ; and so on through endless alterations. 

 Colias Edusa produces Colias Helice, and Colias Helice produces 

 Colias Edusa. Then among the Aphides we have alternations of 

 generations with great regularity, of which Mr. Walker would furnish 

 much more information than any other entomologist. Even the com- 

 mon gooseberry grub of the spring becomes the currant grub of the 

 autumn ; it eats other food and until lately has borne another name. 

 How wonderful are these things ! How worthy of our investigation ! 



The question of uniting or keeping separate the Phryganidae and 

 Lepidoptera is still unsettled. The presence of scales or hairs is 

 perfectly valueless as distinctive, or Mormonia must be a Lepidopteron 

 and Psyche a Phryganea : the more this subject is investigated the 

 more difficult does it become to draw any definite line of demarcation. 

 There is no lepidopterous or phryganidous character that possesses 

 the important attribute of constancy ; and no one, as I have lately 

 shown, has yet attempted to fix the systematic position of Acentria by 

 actual investigation and comparison of all its characters. The immense, 

 the insuperable difliculty of separating these groups leads me to the 



