DIDYCTIUM ZIGZAG. 197 



cottoii- worms were destroyed after they were found showed that they 

 could not have been preyed upon long prior to the date of observation. 

 On the other hand, it is difficult to see how these parasitic larvae with 

 their sluggish habits could find the means of migrating from one cottou- 

 worm to another, as it seems probable that they must do after devouring 

 the individual upon which they are born. The whole question is one of 

 considerable interest, but cannot be solved without further observa- 

 tions. 



THE PROCTOTRUPID PARASITE OF THE COTTON WORM (Didyctium 



zigzag, Kiley). September 10, 1879, a number of small parasitic flies 

 issued from chrysalides of the cotton-worm. Upon examination these 

 proved not to be Chalcids, but to belong to the allied family Proctotru- 

 pidae. The members of this family differ from the Chalcids in their usu- 

 ally slenderer body and longer antennae. The antennae, also, are not 

 elbowed as in Chalcididae. It is a family of very minute species, which 

 are all supposed to be parasitic, many of them upon the eggs of o^her 

 insects. 



The species under consideration is shown at Fig. 43. These flies are 

 black, polished, with the antennae and legs dark 

 yellow. The antenna of the female are 13-jointed, 

 the first joint club-shaped, the second almost globu- 

 lar j 3 to 7 are much thinner than any of the oth- 

 ers ; 3 about as long as 2 ; 4 to 7 almost globular ; 

 4 a little thinner at base ; 8 to 12 about equal in \ 

 size, round at base, and squarely cut off at apex ; 

 13 as long as preceding, ending in a rounded blunt 

 point. The antenna of the male are very long, FIG. 43. Didyctium zig- 

 about as long as the whole insect. The wings 

 are clear and sparsely beset with short, blackish bristles, and with quite 

 a long fringe around the edge. The veins of the wings are yellowish. 



These insects are about .06 of an inch (1.5 mm ) in length. 



These parasites were bred only upon a single occasion. Then many 

 specimens were mounted. Whether they were all from one chrysalis or 

 not it is impossible to say with certainty, but the probabilities are that 

 they were, and it seems probable also that it is not a common parasite. 



The specimens were handed to Professor Eiley for determination. 

 He deemed it necessary to found a new genus for them, of which the 

 following are the characters. A specific description follows the generic. 



DIDYCTIUM, nov. gen. Head, transverse; three ocelli approximate and triangularly 

 arranged; labial palpi 3-jointed; palpi 3-jointed ; antenna? inserted in front and close 

 together, in the 9 hardly reaching to the abdomen ; 13-jointed, the two basal points 

 stout, joints 3-7 suddenly narrowed and together not much longer than 1 and 2, 

 3 being twice as long as the others, 8-13 nearly twice as stout, peduncled, subequal in 

 length, very slightly narrowing toward tip; in the $ as long as body, 15-jointed, 

 joint 3 twice as long as any of the others, 4-13 subequal in length. Thorax as long as 

 abdomen, slightly wider in the middle than the head ; scutellum prominently raised, 

 subovate and marginally ridged ; legs with the tarsi uniformly 5-jointed; front wings 



