298 bulletin: museum of compakative zoology, 



formed, whereas in the first maturation the deep centriole might be 

 termed the Anlage for the whole of the young achromatic figure of the 

 second maturation. 



Chromosomes. In the indirect process in Haminea there is a definite 

 telophase following the formation of the first polar cell. The wall of 

 the nuclear vesicle in the cases observed (Plate 7, Figs. 38, 40-45, 47, 

 48) was formed from substance that was destitute of the granular 

 constituents of the rest of the cytoplasm. This diff"erentiated substance, 

 in which the spindle and chromosomes lie, has been described under 

 various names, — archoplasm, karyoplasm, hyaloplasm, etc.; it is from 

 this substance, whatever called, that the wall of the nucleus is produced. 



The formation of a nucleus between the first and second maturation 

 has been observed to occur in other animals, as follows : in bony fishes 

 by KupfFer und Benecke ('78); in Petromyzon planeri by Boehm 

 ('88, p. 637), who terms this nucleus "eine provisorische Eikern;" in 

 pulmonate molluscs by Garnault ('88-89, p. 13), who terms it "noyau 

 vesiculeux intermediaire ;" in molluscs and Echinus microtuberculatus by 

 Boveri ('90, p. 38), who describes it as a " blaschenformige Kern ; " and 

 in Allolobophora foetida by Foot ('97), who found it occurring in one 

 instance. The appearance of this nucleus in Haminea is similar to that 

 shown by Boveri ('87, '88) in the telophase of the second maturation 

 in Ascaris megalocephala. In Ascaris the chromosomes at first remain 

 distinct, but they become connected with the wall of the vesicle by liniu 

 fibres, just as they do in Haminea. Moore ('95) found that in Elasnio- 

 branchs, after the close of tlie first and second spermatogenic periods, 

 the chromosomes came to lie in vacuoles. Sutton (:00) finds that in 

 the spermatogonial division of Brachystola each chromosome may be 

 converted into a separate vesicle. And, finally, in the spermatogenesis 

 of Paludina (Meves, :0l), each chromosome becomes vacuolated, and may 

 either remain distinct or become fused with others to form an irregular 

 nucleus. 



In Haminea the chromosomes divide before the mantle fibres penetrate 

 the nucleus. The division in this case seems, therefore, to be an act in- 

 dependent of the mantle fibres. 



A quantitative reduction of the chromatin is evidently accomplished 

 by the formation of the two polar cells ; but it is difficult to imagine 

 how any qualitative reduction can have taken place. Recent results in 

 experimental cytology tend to show that the individuality of the chromo- 

 somes has not been established for all cases. It has been shown in 

 Haminea (p. 231 ff") that the chromosomes pass through stages which 



