580 SIDNEY I. KORNHAUSER 
If, now, we examine parasitized males, which have retained 
the more striking tertiary sexual characteristics of color, form, 
and size (figs. 38 and 39), we find that they, too, generally have 
much reduced genitalia. Occasionally, male colored individuals 
with parasites present only a partial reduction of the gona- 
pophyses and these most probably represent those parasitized 
shortly before their mcult to the adult form (figs. 36 and 37). 
The above facts show that the genital appendages are very 
sensitive to the influence of Aphelopus, being reduced even in 
individuals in which the effect of the parasites was not sufficient 
to alter the pigmentation of the pronotum or face. 
In parasitized females, all three pairs of genital appendages 
show a great reduction in size (figs. 30 and 31). They are some- 
times weakly chitinized, bent, and misshapen. The ovipositor 
(fig. 30, gn. 9) does not always form a tube, but consists of two 
separate plates diverging distally. All three pairs of append- 
ages are reduced proportionately, there being no one pair as 
little affected as the ventral valves of the male genitalia. 
The above facts show that, although there is a decided reac- 
tion of the external genitalia due to parasitism, vet there is not 
the slightest tendency of these appendages to assume the char- 
acteristics of the opposite sex. They are, therefore, entirely 
different in the male from the extragenital secondary characters 
in their behavior. The reason for this is to be sought in a con- 
sideration of the origin and development of these two cate- 
gories of characteristics. The extragenital secondary or tertiary 
sexual characteristics, such as color of pronotum and face, ar- 
rangement of spines on the abdominal sclerites, and many others, 
arise during the fifth nymphal instar and make their first appear- 
ance in the adult Thelia. If the nymph be a male and contain 
well-grown Aphelopus larvae, the resulting adult will exhibit 
female extragenital sexual characteristics; but the genitalia, 
though greatly reduced in size, will unquestionably remain male 
in character, because these appendages did not arise in the fifth 
nymphal instar, but were laid down early in ontogeny, either 
before the parasites were present or while the parasites were 
minute and incapable of exerting any marked influence. 
