28 J. T. PATTERSON 



entirely by the inner membrane or envelope. The constriction 

 or ingrowth of the polar membrane does not take place until 

 somewhat later. 



The method of division in the formation of tertiary masses 

 is exactly similar to that just described for the secondaries. No 

 further details are therefore necessary. The formation of the 

 tertiaries may begin as early as the end of the fourth day (fig. 

 73), and continues through the sixth day. From the seventh 

 to the tenth day the multiplication of the tertiary masses and 

 their components goes on with great rapidity, and by the eleventh 

 day they form a very complex structure, which is sometimes 

 surrounded by adipose tissue developed from the host cells 

 (fig. 72). 



Figures 63 to 68 represent a series of tertiary masses which 

 have been set free into the body cavity of the caterpillar. They 

 show the various steps in the multiplication of the com- 

 ponents of a tertiary mass. Figure 63 is a mass containing a 

 single embryonic cell. It has just been set free from the main 

 body of the polygerm. Figure 64 is a slightly later stage in 

 which the embryonic cells are multiplying. In figure 65 a ter- 

 tiary has recently divided, and the component on the right has 

 two cells which have not yet completely separated. Figure 

 66 is a tertiary component with four cells. Figure 67 is of in- 

 terest in that it shows how the embryonic cells are being iso- 

 lated. Ingrowths from the inner membrane have separated 

 the embryonic cells into groups. In some instances only a 

 single cell is thus separated, but usually there are two or more 

 cells in each group. The formation of these groups is then 

 followed by constrictions of the inner and outer membranes, 

 which results in producing many new components of the ter- 

 tiary masses (fig. 68). The components may later completely 

 separate from each other, becoming scattered throughout the 

 body cavity of the host and forming new centers of prolifera- 

 tion. The rate of their distribution to various parts of the body 

 cavity to a very great extent depends upon their relation to the 

 host tissues. If the polygerm is embedded in adipose or other 

 tissue, the scattering of the tertiary masses and their compo- 



