34 2 J- T. PATTERSON. 



found in 12 sections; the single specimen measures 179 /x by 95 /JL 

 and occupies 8 sections only. 



In structure the three polygerms are practically identical. 

 Each consists of two distinct zones: (i) An outer relatively 

 thick zone containing a large number of nuclei irregularly placed, 

 and (2) a central region containing the embryonic nuclei (Fig. 

 19). In the absence of the earlier stages, it is not an easy matter 

 to interpret the conditions seen in these polygerms. In the main 

 they correspond most nearly to the conditions in the egg of 

 Litomastix (Copidosoma} truncatellus , as described by Silvestri 

 ('06). I therefore interpret the outer zone to be the product of 

 the "polar ooplasm" plus the "polar nuclei," while the central 

 region contains the true embryonic nuclei, derived from the 

 fertilized nucleus, or in the case of parthenogenetic development, 

 from the matured egg nucleus. 



There is of course one essential difference in the corresponding 

 stages of Litomastix and Copidosoma. In the polygerm of the 

 former the central region is composed of a solid mass consisting 

 of distinct cells, while in the latter this region is on the point of 

 being broken into multi-nucleated masses, which form the pri- 

 mordia of the embryos (cf. Fig. 19 A with Silvestri's Fig. 33, 

 PI. III.). It may be that the embryonic nuclei are delimited 

 by cell walls in Copidosoma, although one can not make them 

 out with certainty, even under the highest powers of the micro- 

 scope. Judging from the work of other investigators, one would 

 expect to find the embryonic nuclei surrounded by cell walls. 

 In Ageniaspis, Marchal ('04) first reported that the early embry- 

 onal masses were pluri-nuclear in character, but Silvestri ('08) 

 and Martin ('14) have later demonstrated that the nuclei are 

 surrounded by cell walls. In Copidosoma the embryonic nuclei 

 are often so closely packed together that the demonstration of 

 cell walls would be extremely difficult. 



The three polygerms mentioned above are of particular interest, 

 in that they show very clearly the manner in which the central 

 mass with its nuclei breaks up to form the primordia of the 

 multiple embryos. The central region itself consists of two 

 distinct substances, (i) A granular protoplasm in which the 

 embryonic nuclei lie, and (2) a more fluid-like material which 



