HYMENOPTERA 929 



scribed it, the planidium, from the Greek meaning diminutive wanderer. The 

 planidea of the species of three genera have been described. Two of these, 

 Orasema viridis, described by Wheeler ('07a) and Psilogaster fasciiventris de- 

 scribed by Brues ('19) are parasites of ants, and Perildmpus hyallnus described by 

 H. S. Smith ('12) is a secondary parasite of the tachinid and ichneumonid para- 

 sites of the fall webworm. The planidium figured above was found by Miss 

 Norma Ford within the bodies of dissected specimens of one of the meadow- 

 grasshoppers, Conocephalus fasciatus; it is probably a secondary parasite of some 

 parasite of the grasshopper (Ford '22). 



The development of Perilampus hyalinus will serve as an illustration of the 

 life-cycle of these remarkable parasites. The egg has not been observed, but it 

 seems probable that it is deposited upon the food plant of the fall v/ebworm in the 

 vicinity of a colony of this insect. The planidia, which measure less than 0.3 mm. 

 in length and are therefore almost invisible to the unaided eye, were found first on 

 the exterior of the caterpillars; later within their bodies, having bored through the 

 cuticula of the caterpillar by means of their well-developed mandibles, still later 

 the planidia were endoparasitic within the larvae of parasites of the caterpillars. 

 After feeding for a time the planidium molts; the second instar is ovate in shape, 

 with the head bent underneath. After another short period of feeding the larva 

 molts a second time and becomes greatly changed in form (Fig. 1168). Finally 

 after the primary parasite has left the caterpillar and pupated the larva of Peril- 

 ampus becomes an ectoparasite. It then soon completes its growth and pupates. 



Family CHALCIDID^ 



The chalcid-flies are now regarded by most authorities on the 

 Hymenoptera as constituting a single family, the Chalcididce, the 

 distinctive characteristics of which are those of the superfamily 

 Chalcidoidea given above. 



This family has been divided into a score, more or less, of sub- 

 families, which are regarded as families by some authors. For a dis- 

 cussion of the characteristics of these subfamilies the student is re- 

 ferred to the special works on chalcid-flies; among these are Ashmead 

 ('04), Schmiedeknecht ('09), and Viereck ('16). Space can be taken 

 here to mention only a few of the subfamilies. 



Subfamily LEUCOSPIN^ 



The rnembers of this subfamily agree with the Vespidae and differ 

 from all other H}Tnenoptera, except the Gasteruptionidse and the genus 

 Galesns of the family Belytidas, in having the fore wings folded longi- 

 tudinally when at rest. They are also peculiar in having the ovipositor 

 of the female curved up over the dorsimi of the abdomen, often reach- 

 ing the scutellum. These insects are parasitic in the nests of bees. 

 Our most common species is Leucospis afflnis, which measures from 

 6 to 12 mm. in length. It has been bred from nests of a leaf-cutter 

 bee, Megachile. 



Subfamily CHALCIDIN^ 



This family includes chalcid-flies in which the hind femora are 

 greatly swollen and usually dentate or serrate. In this respect they 

 resemble the Leucospinse, but they differ from the Leucospinae in not 



