THE CHALCIDOID GENUS PERILAMPUS. 41 



ventral side, situated in the elastic integument connecting the 

 chitinized plates, are two stigmata, apparently the only spiracular 

 openings in the whole tracheal system. Third segment similar to 

 preceding, the two dorsal spines being considerably farther apart; the 

 ends of the chitinous plate, however, are of quite a different type; 

 instead of ending in a serrate margin the inner margin is smooth, but 

 the posterior corner terminates in a long tapering nrojection con- 

 siderably longer than the width of the chitinous sclerites; laterad of 

 the long tapering projection referred to above are two or three much 

 smaller ones, also situated on the apical margins of the segment; 

 between the ends of the chitinous plates, as in preceding segments, 

 are several hooklike motor appendages, smaller and fewer in number, 

 however, than in the second segment; an additional series of hooks 

 wliicli is not provided in preceding segments is situated just laterad 

 of these. The fourth segment seems to have no dorsal spines; there 

 are two ventral ones, however, situated at the extreme outer margin 

 of the ring; the chitinous plate terminates as in the third segment; 

 motor appendages as in third segment but fewer in number. The 

 fifth segment differs from the fourth apparently only in the possession 

 of a pair of dorsal spines and in the smaller number of ventral motor 

 appendages. The sixth segment does not have the dorsal spines but 

 in other respects is similar to the fifth; the seventh segment possesses 

 the dorsal spines; the eighth does not, nor does the tenth, eleventh, or 

 twelfth; these latter, however, are similar in other respects, excepting 

 that they become gradually less in size. The last segment is provided 

 with an un jointed stylet on each side attached at about the middle of 

 the segment, this stylet about twice the length of the segment itself. 



HABITS OF PLANIDIUM. 



Starting with the planidium upon the skin of the caterpillar, this 

 makes its way tlirough the thinner portion of the integument found 

 at the junctures of the segments, this passage being effected by means 

 of its well-developed mouth parts and speciallya rmored head. Just 

 how the search for the host parasite is conducted is not known 

 excepting as it may be deduced from dissections of preserved material. 

 The planidium has been found in almost eveiy part of the caterpillar 

 and it appears that its search for a host is rather thorough and 

 extensive. The time of its attack upon the host larva has not been 

 very definitely determxined, although from the data at hand it seems 

 most hkely that this follows at once upon the finding of another 

 parasite witliin the caterpillar. This supposition is substantiated by 

 the fact that the planidium is found within the very young tachinid 

 larvae which have just completed their first molt. In this stage the 

 disparity in size between the larvse of Perilam'pus and of Varichseta 

 is very much less than it is later, and it seems remarkable that the 



