38 H. L. WIEMAN. 



the metaphase of a true division, but is distinguished from it by 

 the persisting nuclear membrane and the position of the chromo- 

 somes at one end of the nucleus near the broad end of the cell. 

 No nuclear division takes place but the nucleus becomes oval in 

 shape and the chromosomes generally contract to form a compact 

 mass lying across its center. In some cells at least this chromatin 

 mass seems to divide — one half passing to each side of the oval 

 nucleus. The chromatin may finally disperse and give rise to a 

 condition resembling the first spermatocyte in which the chro- 

 matin has begun to appear. "Possibly the division of the chro- 

 matin inside the nucleus, which occasionally seems to occur, is 

 the persistent remnant of a true nuclear division, or it may be 

 compared with the 'intranuclear karyokinesis ' described by 

 Kostanecki in the parthenogenetic eggs of Mactra" (p. 93). 

 Toward the end of the rest stage the chromatin becomes grouped 

 in the form of large elongate granules or small bands having a 

 more or less meridional arrangement under the membrane. 



The second spermatocyte division in Neuroterus is a true mi- 

 totic division in which the haploid number of chromosomes, 10, 

 appears on the spindle to be equally divided between the daughter 

 cells. There is also a small stained body lying outside of the 

 spindle which passes undivided to one of the spermatids. 



In the spermatogonia and in mitotic figures of nerve cells in 

 the developing nervous system Doncaster finds the halpoid 

 number of chromosomes, 10, but in mitoses of immigrant meso- 

 derm cells the diploid number, 20. 



The eggs layed by the females of the bisexual generation 

 undergo two maturation divisions; leaving 10 chromosomes for 

 the female pronucleus. The spermatozoon brings into the egg 

 10 chromosomes, and 20 chromosomes appear on the cleavage 

 spindles. The parthenogenetic eggs of the female generation 

 may be divided into two groups: Those which undergo matura- 

 tion and develop into males; those which omit the maturation 

 divisions and develop into females. In the first group 10 chro- 

 mosomes are found in the cleavage divisions ; in the second group 

 20. Since any female produces only one kind of egg, there are 

 male-producing females and female-producing females. 



Mitoses in the nervous system of all females show the diploid 

 number of chromosomes. 



