DEVELOPMENT OF PAEACOPIDOSOMOPSIS 31 



tertiary masses. Numerous cases similar to these have been 

 observed. In late stages the embryonic masses break out from 

 the ganglion and become scattered throughout the body cavity, 



I have noticed from my records that most of the cases of 

 ganglionic infection, especially in the head region, arise in host 

 eggs that were parasitized during the late embryonic period, 

 just before the young caterpillar hatches. This is probably to 

 be explained by the position of the host embryo in the egg. At 

 the time of hatching the head of the caterpillar is situated at 

 the apex of the dome-shaped egg, and it is at or near this point 

 that the female parasite inserts her ovipositor at the time of 

 laying. 



The polygerm is often surrounded or embedded in fat tissue 

 developed from the host cells. The fat tissue probably starts 

 to develop from mesenchyme cells such as are shown in figures 

 49 and 50. The adipose tissue not only serves as a source of 

 nutriment for the growing polygerm, but it also holds the embry- 

 onic masses together (figs. 72 to 75), and thus delays their 

 dispersal. 



The relation of the host tissues to the parasitic egg is all impor- 

 tant in the development of the latter. It can be shown that the 

 development of the parasitic egg is dependent upon the growth 

 of the host embrj'o. This has been demonstrated in the fol- 

 lowing way. A batch of eggs laid in the laboratory by a virgin 

 female moth were exposed for an hour to a brood of female para- 

 sites. Several parasitic eggs were deposited in each host egg. 

 Two days "later these eggs were fixed and sectioned. The moth 

 eggs of course did not develop, and an examination of the sec- 

 tions revealed the fact that not a single parasitic egg developed. 

 Under similar conditions, but with fertilized moth eggs, all of 

 the parasitic eggs would have been in late cleavage stages. 



c. Dissociation of the polygerm 



I have already stated that at some period in its history the 

 polygerm undergoes fragmentation or dissociation. The point 

 at which dissociation occurs varies greatly in different cases. 



JOURNAL OF MORPHOLOGY, VOL. 36, NO. 1 



