DEVELOPMENT OF PARACOPIDOSOMOPSIS 29 



nents may be greatly delayed (fig. 72) . On the other hand, if 

 the polygerm happens to lie free within the body cavity, the 

 dispersal of its components may begin very early, even as early 

 as the primary mass stage. 



b. Relation of parasitic egg to host tiss^ies 



To understand fully the account of the distribution of the 

 products of the polygerm, it is necessary to call attention to 

 the relation of the parasitic egg to the host tissues. The ques- 

 tion is one of the greatest interest, for it can be demonstrated, 

 by the means of a very simple experiment, that the development 

 of the parasitic egg is dependent upon the development of the 

 host egg. Not only is this true for the late stages, but also for 

 the initial steps in development. 



Marchal ('04), Silvestri ('06), and Martin ('14) have all made 

 note of certain points on the relationship of the parasitic egg to 

 the host. In the case of Ageniaspis, Marchal states that in 

 order for the egg to develop completely it is essential that it be 

 placed within the embryonic region of the developing caterpil- 

 lar (Hyponomentus) . In all of his preparations showing the egg 

 of Ageniaspis, he always found it in the body cavity of the em- 

 bryo, where it normally develops. However, he states that his 

 preparations are not numerous enough to determine definitely 

 whether or not some eggs are lost or die if placed in an unfavor- 

 able position, such as the intestine or yolk. He implies that 

 some are thus lost, since it does not seem probable that the 

 parasite could find, by means of its probe, the most favorable 

 region in which to place the egg. In later stages he discovered 

 that the epithelial layer which at first forms a cyst about the 

 developing egg, and then gives rise to the elongated tube of the 

 chain of embryos, is the product of the host tissue. In the case 

 of Polygnotus minutus, Marchal discovered the interesting fact 

 that the egg is lodged in the gastric pouch or stomach of the 

 host (Cecidomyia), and there, curiously enough, undergoes 

 its development. 



