366 J- T. PATTERSON. 



second envelope, which lies just inside the nucleated membrane. 

 Apparently, this inner envelope is formed from the peripheral 

 layer of cells of the embryonic mass (Fig. 3). The primary 

 embryonic masses produce secondary masses by fission. A very 

 clear case of division is seen in Fig. 8, on the right. 







III. ORIGIN OF THE ASEXUAL LARV/E. 



The first sign of asexual larvae appears in young polygerms 

 between seventy-five and eighty hours old. One of the youngest 

 stages observed is shown in Fig. 3. An asexual embryo lies at 

 the upper end of the figure, and is distinguishable from the 

 primary masses by two features of its organization. First, the 

 asexual embryo is composed of a large number of relatively small, 

 closely packed cells, whereas a primary mass is composed of a 

 few large cells, showing no definite arrangement. Second, the 

 inner of the two envelopes surrounding the embryo is decidedly 

 hicker than the corresponding membrane of a primary mass. 

 Both of these features become more evident in slightly older 

 stages, such for example, as that shown in Fig. 4. In this speci- 

 men the asexual embryo stands in striking contrast to the rest 

 of the polygerm. Furthermore, the constriction of the nucleated 

 membrane, or outer envelope, has all but cut off the embryo from 

 the primary masses. A similar condition is seen in Fig. 5. 



At this point it will be well to recall Silvestri's account of the 

 origin of the asexual larvae in Litomastix. The polygerm of 

 Litomastix, soon after the nucleated membrane is established, 

 begins to show differentiation into two distinct regions. The 

 anterior region is made up of large and small cells, while the 

 posterior region is composed of small cells only. A constriction 

 appears in the nucleated membrane, which finally separates these 

 two regions. Silvestri names the anterior region the massa 

 germinigena, and the posterior the massa monembrionale. The 



* 



latter subsequently differentiates into a single asexual larva. 

 In the course of further development, the massa germinigena 

 gives rise to a few secondary monembryonal masses, which 

 differentiate into asexual larvae, and to a large number of other 

 masses. This is accomplished by constrictions in the polygerm. 

 The masses continue to multiply by constrictions, and may from 



