300 



TRANS. ST. LOUIS ACAD. SCIENCE. 



spun in association they are held' 

 together by this loose silk either 

 irregularly, or in regular single 

 row or double row, and the loose 

 silk may be so abundant as to look 

 like matted masses of cotton or 

 wool, and to almost or entirely 

 hide the individual cocoons (Fig. 

 5). Exceptionally the texture of 

 the cocoon is leathery and the sur- 

 face ribbed, while in a few cases 

 the sides are flattened. In the case 

 of Apanteles acronyctce no defi- 

 nite cocoon is formed, but the lar- 

 Fig. 5. — Mass of Microgaster cocoons VcB transform promiscuously in a 



with rib of a leaf drawn around them. j^^SS of silk. In Color there is CVery 



variation through silvery-white, dull opake white, cream-color 

 and different shades of yellow to brown. 



The peculiar manner in which the Microgasters infesting Phi- 

 lampelus spin their smooth cocoons has been described in the 

 "American Naturalist" for 187S, vol. xii. pp. 558-60. Mr. J. P. 

 Marshall, describing the species parasitic upon Philampelus, 



9 10 11 12 13 



Fig. 6.— Formation of smooth cocoon by the larva of Microgaster. (After Marshall.) 



states that the first act of the Microgaster upon emerging from the 

 caterpillar is to attach its posterior end to its host by some silken 

 threads, as shown in Fig. 6, ^. It then forms a series of loops of 

 silk, as shown greatly enlarged in Fig. 7, moving its head altern- 

 ately from left to right and then from right to left. After spin- 

 ning to the top of the cocoon (Fig. 6, ^) the larva reverses its- 

 position so as to rest with its head down (Fig. 6, ^), when it 

 spins the other side of its cocoon, gradually contracting its body 



