SEXUAL CHARACTERISTICS OF THELIA 589 
ancient type of genitalia found in practically all primitive ho- 
mopterans. Funkhouser (’17) considers that the family Mem- 
bracidae is the lowest of the Homoptera with the exception of 
the Ciecadidae. One of his four reasons for this assumption is 
that in the Membracidae ‘‘the genital organs are simple. Little 
progress has been made in developing these structures from an 
ancient type.” Considering, then, that the gonapophyses of 
Thelia are still of the same type as that established when the 
order Homoptera evolved in the distant past, we see why, under 
the effects of parasitism, they remained more constant than did 
the extragenital sexual differences. The formation and sexual 
differentiation of these appendages are started before the para- 
sites are present. The mechanism once under way is not re- 
versed by parasitism, but the resultant products are greatly 
reduced in size and suffer, as will be shown, the loss of certain 
adult characteristics specific for Thelia bimaculata. 
Giard (’89) pointed out that parasitized individuals of Typh- 
loeyba showed a reduction of the external genitalia in both 
sexes. The male of Typhlocyba hippocastani has a very com- 
plicated oedagus produced into eight branches at its distal end, 
and this organ is specific for hippocastani, distinguishing it 
nicely from T. douglasi. Males parasitized by Atelenevra show 
a reduction of the branches of the oedagus to six, four, or three. 
Thus the specific character of the oedagus is ‘profoundly modi- 
fied,’ so that parasitized hippocastani may be confused with 
Typhlocyba rosae L. or Typhlocyba lethierryi J. Edw. 
The specific characteristics of the gonapophyses first appear 
in the final molt, and they are probably recent from a phylo- 
genetic standpoint. As other specific characteristics, one would 
expect that they would fail to develop or develop but partially 
in parasitized individuals. Thus a comparative study of the 
gonapophyses of Thelia bimaculata Fabr. and its nearest avail- 
able relatives was undertaken, to ascertain if bimaculata pos- 
sessed any specializations which might be looked upon as specific 
modifications. Through the generosity of Dr. E. D. Ball various 
membracids of the tribe Telamonini were made available, and 
these fortunately included the rare Thelia uhleri Stal. Normal 
