10 J. T. PATTERSON 



first polar body division may either precede (fig. 28) or follow 

 (fig. 4) the second maturation division. Consequently, there 

 is no close correlation between the two divisions. This is exactly 

 the condition in Ageniaspis as reported by Martin. 



Each of the tw^o divisions is equational in character. In 

 figure 28 is a remarkably clear case of the late anaphase stage 

 of the first polar body division. At each pole of the spindle 

 are eight distinct chromosomes (Ai, A2). In figure 29 the ootid 

 (^2) shows eight chromosomes, and in the second body (Bi) 

 seven are visible. Doubtless one of the chromosomes is hidden 

 by some of the other seven, for in other figures one can count 

 eight in the second polar body (fig. 31, Bi). The result of these 

 two divisions is the formation of four groups of chromosomes, 

 of which three are polar bodies (fig. 29, Ai, A2, Bi) and one the 

 ootid (S2). The latter forms the female pronucleus. 



3. The formation of the polar nucleus. At this point we shall 

 describe the formation of the polar nucleus, which is destined to 

 play an important role in the development of the polygerm. 

 This body was first described, under the term paranucleus, in 

 the egg of Ageniaspis by Marchal ('04), who failed to observe 

 its formation, but who gave a very good account of its later 

 history. 



It was next described by Silvestri for the egg of Litomastix. 

 The process of maturation in this species is identical with that 

 of Paracopidosomopsis. Consequently, at the close of matura- 

 tion the egg of Litomastix contains, in addition to the nucleo- 

 lus and the female pronucleus, three masses of chromatin lying 

 close together, but distinct from one another. These are the 

 three polar bodies. In connection with his account of the first 

 and second cleavages, he makes the following brief statements 

 concerning the origin of the nucleolus from the polar bodies: 

 That the three polar nuclei, "which during such a period are 

 close together, fuse together to form a single mass of chromatin, 

 a nucleus without membrane and with the chromosomes con- 

 densed" ('06, p. 14); and later, ''During this stage the chroma- 

 tin mass of the polar bodies is formed into a complete nucleus 

 with membrane and reticulum very distinct, and is always found 



