408 ORDERS OF PTILOTA. 



itself; the prothorax and mesotliorax are very short, form- 

 ing only two narrow rings, to each of which, on the under 

 side, a pair of legs is attached ; the mesothorax is very greatly ' 

 developed, and divided by several oblique sutures ; the legs 

 are short, slender, and compressed, with the tarsi furnished 

 with fleshy cushions, but destitute of claws; the two anterior 

 pairs of legs are close together, and the posterior pair very 

 far behind ; the abdomen is small, and scarcely coriaceous ; 

 it is cylindric, eight or nine-jointed, and furnished with a re- 

 curved point. 



These insects are of small size, and in the larva state they are 

 parasitic in the bodies of various species of wild bees (Andrenidce), 

 and wasps (Vespidce). The order was first detected by Rossi, an 

 Italian entomologist, who discovered its habits, and formed a genus 

 for the reception of the species which he discovered {Xenos vespa- 

 rum, Rossi ; Xenos Rossii, Kirby), but he regarded it as belonging 

 to the order Hymenoptera. Mr. Kirby having discovered another 

 species belonging to the same group, but to a distinct genus, in 

 this country, and having received another species from Professor 

 Peck of America, investigated the subject very minutely, and de- 

 tailed the characters of the order and its genera in an elaborate 

 Memoir published in the Linnajau Transactions. The following is 

 Mr. Kirby's account of his discovery of the English species, and as 

 it is illustrative of the habits of the insect, I shall quote it at 

 length. Having observed upon various species of Andrena " some- 

 thing that I took to be a kind of acarus, which appeared to be 

 immoveably fixed just at the inosculations of the dorsal segments 

 of the abdomen, and at length finding three or four upon a speci- 

 men of Melitta {Andrena) nigrocenea, I determined not to lose the 

 opportunity of taking one off to examine and describe ; but what 

 was my astonishment, when, upon my attempting to disengage it 

 with a pin, I drew forth from the body of the bee a wbite fleshy 

 larva a quarter of an inch in length, the head of which I had mis- 

 taken for an acarus ! After I had examined one specimen, I 

 attempted to extract a second, and the reader may imagine how 

 my astonishment was increased, when, after T had drawn it out 

 but a little way, I saw its skin burst, and a head as black as ink, 

 with large staring eyes and antennae consisting of two branches, 

 break forth and move itself briskly from side to side. It looked 

 like a little imp of darkness just emerged from the infernal regions. 

 My eagerness to set free from its confinement this extraordinary 

 animal may be easily conjectured. Indeed, I was impatient to be- 



