BIOLOGY OF PARACOPIDOSOMOPSIS. 367 



time to time produce a few asexual embryos; but a large majority 

 of them differentiate into sexual embryos. 



Some phases of the development of Paracopidosomopsis are 

 directly comparable to certain stages of Litomastix. The forma- 

 tion of the primary masses and their subsequent mode of multi- 

 plication is very similar to the history of the massa germinigena. 

 The chief difference is the early formation of a monembryonal 

 mass in Litomastix, for which there is no counterpart in Paraco- 

 pidosomopsis. According to Silvestri the young polygerm always 

 differentiates into a monembryonal mass and the massa germini- 

 gena. In the American species a single asexual embryo may be 

 found at an early stage (Figs. 3, 4, 5), but this is by no means 

 the universal rule. In Figs. 6, 7, 8 are shown three well-developed 

 polygerms in which no asexual embryos have as yet appeared. 

 It is not certain whether such polygerms later produce asexual 

 larvae, although the evidence seems to indicate that at least some 

 of them do. In some cases two or more asexual embryos may 

 develop simultaneously in the very young polygerm. The speci- 

 men on the right of Fig. 9 has two such embryos, and Fig. n 

 illustrates a similar case. The polygerm shown in Fig. 13 has 

 given rise to four asexual embryos, all in the same stage of de- 

 velopment, but situated in different parts of the mass. 



These facts indicate clearly that the polygerm of Paracopido- 

 somopsis may give rise to one or more asexual embryos at a very 

 early stage of differentiation, but there is no such regularity in 

 the formation of a single monembryonal mass as reported by 

 Silvestri for Litomastix. 



IV. DISSOCIATION OF THE POLYGERM. 



We have already mentioned the fact that the primary masses 

 divide to produce the secondary masses. An early phase of this 

 process is seen in Fig. 6. The primary mass at the extreme left 

 and the one lying on the lower side has each undergone several 

 divisions. There are at least four secondary masses visible in 

 the median section of each primary center. In a still younger 

 stage, Fig. 8, the primary mass on the right is just completing the 

 first division. At this stage of development each secondary 

 mass consists of one or more large central cells and an indistinct 



