34 J. T. PATTERSON 



taining one or more of the embryonic cells. The inner membranes 

 then completely form, and thus separate the groups from one 

 another (figs. 67, 68). This method of division becomes more 

 accentuated in the formation of components and the sexual 

 embryos. 



During the thirteenth and fourteenth days the multiplication 

 of the tertiary masses occurs in the manner just described. At 

 the end of the fourteenth day tertiary components begin to form 

 embryonic masses, each of which will produce a single sexual 

 embryo. Figure 76 is a section of a tertiary component lying 

 free in the body cavity, and in which the formation of sexual 

 embryos is in progress. The section shows six masses, in at 

 least four of which further divisions will occur. In many places 

 in the series single embryonic cells are being isolated to form, in 

 all probability, a sexual embryo (fig. 76, X). Owing to the 

 fact that a cell may divide immediately after it is isolated, and 

 usually before the inner membrane is completely organized 

 about it, it is difficult to establish this point. Nevertheless, 

 the evidence revealed in an intensive study of this period of 

 development points to the conclusion that each sexual embryo 

 arises from a single embryonic cell. Just why components con- 

 tinue to multiply up to a certain point and then suddenly cease 

 to divide before producing embryos, is not easy to answer. How- 

 ever, that this point of departure varies in different cases is 

 evidenced by the great variation in the number of individual 

 parasites arising from different eggs. 



By the end of the fifteenth day no further divisions of com- 

 ponents are seen. Each mass represents an individual embryo. 

 Figure 77 shows the typical condition of this period. Each 

 embryo consists of several cells, closely pressed together and 

 surrounded by a well-formed inner membrane. Later, the 

 embryonic cells form a typical morula stage. From the sixteenth 

 to the eighteenth day the embryos become well organized. The 

 inner and outer membranes thin out to form a double-walled, 

 transparent envelope about each embryo (fig. 78). 



On opening up infected caterpillars from the fifteenth to the 

 eighteenth day, one finds floating in the fluid of the body cavity. 



