DELTOCEPHALUS. 49 



As heretofore, in difficult species of Deltocephali, the 

 varying parts of the pygofcr will be used as helps 

 to discrimination ; and, as far as possible, those ex- 

 ternal parts which can be brought into view, without 

 much trouble or requirement of extra manual address, 

 will engage attention. 



Fieber recognises sixty-seven species of Deltocephali 

 in his Catalogue of European Cicadinae, and Dr. Puton 

 increases this list to eighty-nine species ; but John 

 Scott remarks that " some of these probably will sink, 

 though others may take their places." Mr. Edwards 

 admits only twenty-three into his Synopsis, but there 

 seem to me to be reasons in favour of curtailing his 

 his list yet farther. 



It has been before noticed that the winged veining 

 of the Tettigidse is often aberrant, but Mr. J. Edwards 

 says that he has not, in a single instance, found that 

 differences in the form of the genital styles are in any 

 way correlated to the development of the elytra and 

 wings. He places a very high significance on the 

 forms of these styles.* 



The Deltocephalidae, like the Delphacidae, show in 

 several species a singular tendency to complete their 

 reproductive systems before all the stages of their meta- 

 morphoses have been accomplished. Such conditions 

 may be regarded if not of a larval, yet of a nymphal 

 character. Side by side we find fully-winged forms 

 with perfected genitalia ; and other forms, with stunted 

 or aborted wings, not much in advance of the alaB of 

 pupse still in their sheaths. These forms, nevertheless, 

 are fertile. 



The reproductive powers of some larvae have deeply 

 interested many biologists. It would appear that, 

 through some excitation or abnormal activity, certain 

 organs pass through their developmental changes at an 

 increased rate, leaving other organs either in abeyance 

 or simply progressing at their normal rate of increase, 

 so far as time is concerned. 



* Ent. Mo. Mag. xxv. p. 381. 

 VOL. II, E 



