DEVELOPMENT OF COPIDOSOMA GELECHI/E. 345 



fat bodies lying in the middle region of the body cavity of the 

 larval host. If the caterpillar is parasitized one of these bodies 

 is almost certain to contain the polygerm. 



After the elongated condition is attained, the further growth 

 of the polygerm may take place in any direction. In some 

 cases the extension is mainly in one plane, thus transforming the 

 polygerm into a flat, plate-like structure (Fig. 13). In other 

 cases it forms a thick irregular mass (Fig. u), and when viewed 

 as a whole mount shows many elevations on its surface, due to 

 the breaking up of the entire polygerm into single masses, each 

 of which contains an embryo. 



During the rapid expansion of the polygerm a very important 

 change takes place in its structure, whereby each embryo become 

 enclosed in a double involucre. The first step in this process 

 begins just prior to that period of development in which the 

 polygerm attains its elongated, cylindrical shape. It consists 

 in the formation of constrictions in the nucleated membrane 

 which break up the single polygerm into a series of primary 

 divisions or masses (Fig. 15). In the specimen shown in this 

 figure there are about twelve of these masses. Each primary mass 

 has the same general structure as the original single polygerm. 

 It is surrounded by a portion of the nucleated membrane, con- 

 tains precipitated material, and has a variable number of em- 

 bryos, from five to fifteen or more. 



In Fig. 22 one end of a longitudinal section of a polygerm is 

 shown with the completed primary masses. Three of these 

 masses are seen in the figure, together with a portion of a fourth. 

 Attention should be called to the fact that the adipose tissue, 

 although in contact with the polygerm, is still a distinct structure. 

 In the process of forming the primary masses not all of the elements 

 of the nucleated membrane are taken into these structures. 

 Some of them are left behind and later lie in the inter-embryonal 

 spaces or interstices. In Fig. 22 a number of these elements 

 (cells and nuclei) are shown at the point marked " N," lying 

 between the primary masses and the adipose layer. 



In another portion of the same polygerm a single primary 

 mass is being constricted off laterally. It appears as a bud ex- 

 tending from the main body of the polygerm. It is such cases 



