548 



AN INTRODUCTION TO ENTOMOLOGY 



" 2dA 



Fig. 673. — Wing of Paraxenos eberi. 

 (From Pierce, after Sai^nders.) 



in the other families they are two- to four-jointed and without claws. 

 The venation of the hind wings is degenerate. There is a variable 



number of radiating veins, which in the most generalized wings are 



eight in niimber. These are sup- 

 posed, by Pierce ('09), to be the 

 eight principal veins of the typi- 

 cal wing, the costa, subcosta, ra- 

 dius, media, cubitus, and the three 

 anal veins, respectively (Fig. 673). 

 The abdomen is composed of 

 ten segments. 



The adult female is very de- 

 generate in form. That part of 

 the body which projects from the 

 body of the host is the cephalo- 

 thorax, the head and thorax being 

 jonsolidated into a single disk- 

 like region. The abdomen, which 

 is within the body of the host, is 

 a great sac filled with eggs. The 

 body of the adult female is in- 

 closed in the skin of the last larval 



instar, which is termed the puparium; but there is no pupal stage in 



this sex. 



The postembryonic development of the stylopids is very peculiar. 

 In the adult female the eggs are free in the body cavity, where they 

 hatch. The young larv« are campodeiform and active. As they 

 bear some resemblance to the triungulins of the parasitic blister-beetles, 

 they are termed triungulins by some writers ; but as they do not possess 

 three tarsal claws, this term is inappropriate when applied to vhem. 

 For this reason the first instar of a stylopid larva is termed z. iriun- 

 gulinid. 



The stylopids are very prolific; more than 2000 triungulinids pro- 

 duced by a single female have been counted. This fecundity is 

 doubtless correlated with the uncertainty of any individual triun- 

 gulinid being able to find its proper host. 



The triungulinids escape from the body of the female through 

 unpaired median genital apertures on the second to fifth abdominal 

 segments. These apertures open into the space between the venter 

 of the female and the pupariimi, which is termed the brood chamber. 

 The triungulinids escape from this space through a slit in the cephalo- 

 thorax of the puparium, between the head and the prothorax, and then 

 crawl over the body of the host. This is the beginning of the most 

 critical period in the life of the stylopids. For the continued existence 

 of any individual of the brood it must find a larva or a nvTnph of the 

 particular species that is its proper host. This is doubtless accom- 

 plished in different ways in the different species. Those that infest 

 Homoptera and other insects that do not build nests must wander 



