HYMENOPTERA 



321 



integrate if they happen to be placed in the yolk or the intestine of the 

 host embryo. In the newly hatched caterpillar host the egg may be 

 found in any part of the body cavity or imbedded in the tissues adjacent 

 thereto. It is most frequently found in nervous or adipose tissue. The 

 tissue not only serves as a source of nutriment for the growing polygerm 

 but also holds the embryonic masses together and thus delays their dis- 

 persal. The usual time for dissociation and dispersal is during the period 

 in which secondary and tertiary masses are beings formed, i.e., from the 

 fourth to the tenth day. In adipose tissue the masses may remain con- 

 nected until the eleventh day or even later. At the end of the fourteenth 

 day the tertiary components begin to form em- 

 bryonic masses. Each mass will form a typical 

 morula stage from which a single sexual embryo 

 will arise. By the sixteenth to the eighteenth day 

 the embryos become well organized, the inner and 

 outer envelopes thinning out to form a double- 

 walled, transparent capsule about each embryo 

 (Fig. 275). The parasites reach the larval stage 

 between the twenty-second to the twenty-seventh 

 day. They then escape from the capsules into the 

 body cavity of the caterpillar host. Once free, the 

 larvae proceed to devour the contents of the host, 

 eating first the fatty tissue and finally the various 

 internal organs, the last to disappear being the 

 nervous system and the intestine, leaving only the 

 cuticular layer of the body wall. The larvae 

 pupate about the twenty-eighth day. Emergence 

 of the parasites under laboratory conditions occurs 

 on the forty-seventh day. 



Among the embryos that develop, certain 

 individuals are found that lack reproductive, 

 respiratory, and circulatory systems and in which 

 no Malpighian tubules are produced. They are 

 asexual embryos which will never imdergo 

 metamorphosis and are nonviable. In Litomastix asexual embryos 

 can be recognized in young polygerms 70 to 72 hours old. The 

 young asexual embryo differs from other embryonic masses in having a 

 larger number of cells and in having a relatively thicker inner membrane. 

 They arise during both the secondary- and tertiary-mass stages. 

 Although some polygerms produce asexual embryos at a very early- 

 stage, nevertheless the majority of such embryos do not appear until 

 after dissociation has taken place. The asexual larvae apparently per- 

 form no function, invariably degenerate, and do not live over three days 



emb 



Fig. 275. — Litomastix. 

 Advanced stage of the 

 development of the sexual 

 embryos {emb). 



