100 



SATURDAY LECTURES. 



smaller until we have a mere bag, which finally I'alls to the 

 ground, and there lies helpless for a few weeks, during which 

 the mature form which I have described as Tromhidium 

 muscarum, and which has eight instead of six legs, develops 

 under the Astoma skin. The spherical red eggs are laid in 

 loose masses in the ground, and the young Astoma, upon 

 hatching, crawls upon the first fly which offers it an op- 

 portunity. 



To show the transformations I exhibit illustrations (Fig. 



Fig. II. — Trombidium locustartim. — ^r, mature larva when about to leave the 

 wing of a locust ; ^, pupa; c, male adult when just from the pupa; d, female — 

 the natural sizes indicated to the right; e, palpal claw and thumb ; /, pedal claws; 

 g, one of the barbed hairs ; h, the striations on the larval skin. (After Riley.) 



11) of an allied species ( Trombidium locustaruvi Riley,) which 

 similarly affects locusts or "grasshoppers," and I would 

 parenthetically remark that man is as much subject to an- 

 noyance from these red mites as are the fly and locust ; for 

 the irritating pustules so common in late summer and 

 autumn on the limbs of persons who walk in rank grass or 

 along rivers are caused bj^ a minute red mite, {Leptus irritans 

 Riley,) popularly denominated " Jigger," and evidently the 

 six-legged larva of some eight-legged form not yet ascer- 

 tained. 



PARASITISM. 



This external parasitism in insects is, however, less remark- 

 able than that which is internal. 



If I should tell you that I know certain kinds of birds 



