26 J. T. PATTERSON 



only forming. The number of embryonic cells included in a 

 primary mass is extremely variable. I have seen cases where not 

 more than four or five cells were present in a single primary mass; 

 in other cases I have counted as many as fifty. The number of 

 cells included in a primary mass is not a matter of any great im- 

 portance. The embryonic cells are constantly dividing, so that a 

 primary mass with a few cells would soon have that number 

 increased. Furthermore, the primary masses themselves soon 

 divide, especially those which possess a large number of cells. 



Figure 56 represents a further advance in the development of 

 the polygerm. Several of the primary masses are already com- 

 pleted (Pr.M.). One of these is differentiating into an asexual 

 embryo (As.E.). This is the youngest stage in which one can 

 recognize the asexual embryos. A more advanced stage is 

 illustrated in figure 57. The primary masses are practically all 

 completed. There are fifteen of these masses, in addition to a 

 large conspicuous asexual embryo (As.E.) . The polar membrane 

 already shows signs of constrictions, which will result eventually 

 in forming an outer envelope around each mass. 



A completed polygerm is one in which all of the primary masses 

 are found. Such a stage is shown in figure 58. This one has a 

 large asexual embryo and about twenty primary masses. The 

 asexual embryo has both the outer and inner envelopes com- 

 pletely formed, which has resulted in cutting it off from the rest 

 of the polygerm. Each primary mass has as yet only the inner 

 envelope completed. It consists of a distinct, rather thick 

 membrane containing a large number of nuclei (fig. 58, 1.M.C.). 

 The cavity contains a variable number of true embryonic cells, 

 loosely arranged and spherical in shape. 



Figure 59 represents a stage slightly more advanced than 

 the preceding. The section contains no asexual embryos, but 

 a very young one is found in one of the lateral sections of the 

 series. However, asexual embryos are not found in all poly- 

 germs of this age. The polygerm illustrated in figure 60 has 

 no asexual embryo. The significance of this will be discussed in 

 connection with the history of the asexual larvae, given in a 

 later section of the paper. 



