48 



BULLETIN 66, UNITED STATES NATIONAL MUSEUM. 



Male. 



The third instar shows a partial fusion 

 of the first two thoracic segments with 

 the head still separate. Last abdominal 

 segment fused with the preceding, the 

 segment appearing longer and posteriorly 

 narrowed (fig. 13). 



In the fourth instar the anterior end of 

 the head is more pointed, and the eye- 

 spots are smaller; the segments of the 

 thorax are fused; and the rudiments of 

 the legs become more distinct (fig. 14). 



In the fifth instar the head and thorax 

 fuse into acone-like cephalothorax, with a 

 distinct ring suture (fig. 15). 



In the sixth instar the cephalothorax is 

 more differentiated from the abdomen. 

 The anal pore on the tenth and the geni- 

 tal pore on the ninth segments are both 

 distinct (figs. 16, 17). 



The seventh instar is passed within the 

 skin of the sixth and is really a pupa. The 

 appendages become strongly developed. 

 During this stage the puparium is pushed 

 outwards (figs. 18, 19).. 



The second or real pupa forms within 

 the skin of the seventh instar. It is 

 essentially similar to the Hymenopterous 

 pupae (fig. 22). 



The adult male breaks forth from the 

 two pupal skins and thrusts off the cap, 

 or operculum, of the puparium, which 

 was the head of the sixth instar. 



Female. 



The third instar shows a partial fusion 

 of the first two thoracic segments, with 

 the head still sepai-ate. Last abdominal 

 segment fused with the preceding, the 

 segment thus appearing obtuse (fig. 7). 



In the fourth instar the anterior end of 

 the head is more pointed, the head is 

 shorter, with the eye-spots at the posterior 

 edge; the thorax is differentiated from the 

 abdomen and the segments are fused 

 (fig. 8). 



In the fifth instar the head fuses with 

 the thorax forming the cephalothorax, but 

 with the suture discernible (fig. 9). 



In the sixth instar the eyes are not per- 

 ceptible; the cephalothorax is markedly 

 differentiated from the abdomen, flat- 

 tened dorsally, and somewhat widened; 

 the sutures between the segments com- 

 pletely disappear (fig. 10). 



In the seventh instar the cephalothorax 

 is strongly flattened dorsally, depressed 

 and chitinized. The cephalothorax is 

 exserted at this time (figs. 11, 12). 



The adult female is closely inclosed by 

 the integument of the preceding instar. 



ALIMENTATION. 



In various places mention has been made that alimentation is 

 probably by osmosis. All evidence points toward this conclusion, 

 as the internal organs of the host are not injured in any way except 

 by crowding and exhaustion of the juices. The mouth parts may 

 or may not play some part in the function. Osmosis probably occurs 

 equally through all portions of the skin. 



An important observation by Westwood (1840) calls for more 

 extensive studies in the future. He noticed a cord attaching the 

 base of the abdomen to the integuments of the host and suggested 

 that this was a tube through which food was taken by the parasite. 



The writer has frequently noticed some kind of an attachment in 

 specimens extracted by him. The female of Halictoxenos crawfordi 

 has a long tube evidently arising from the base of the abdomen. 



