224 KATHARINE FOOT AND E. C. STROBELL. 



Photos ii, 12, 14, 15 and 17, there is no evidence that such a 

 structure is present. 1 



If the nucleolus in the germinal vesicle of Euschistus corre- 

 sponds to the principal nucleolus of Allolobophora it must be con- 

 ceded that there are marked individual differences between the 

 two, differences quite as marked as those existing between the 

 chromosomes of these two forms. 



INDIVIDUALITY AND CONTINUITY OF THE CHROMOSOMES. 



The investigators who question the individuality and con- 

 tinuity of the chromosomes urge the necessity for further study 

 of the critical stages bearing on this problem the stages occur- 

 ring between the end of one mitosis and the beginning of the 

 next. Meves ('08) holds that during these stages it is impossible 

 to recognize the chromosomes. He says : " Man sucht hier, 

 wie O. Hertwig 1890 geschrieben hat, in den Kern etwas hinein- 

 zudemonstrieren, was kein unbefangener Beobachter in seiner 

 Struktur erkennen wird. 



Pick ('07) claims, that a study of the rest stages proves that 

 the theory of the individuality and continuity of the chromosomes 

 is untenable. 



Tellyesniczky ('07) also makes a strong plea for more thor- 

 ough and careful work on these stages. We are in sympathy 

 with him in his skepticism concerning the individuality and con- 

 tinuity of the chromosomes, but our results differ from his in 

 some, perhaps unimportant, details --differences which may 

 normally exist in different forms. For example Tellyesniczky 

 ('05) believes that a homogeneous distribution of the nuclear sub- 

 stance throughout the nuclear vesicle precedes every mitosis, and 

 the young spermatocytes of our Photos I, 4 and 5 lend support 

 to this claim. The young oocyte of Photo 13 also indicates a dif- 

 fused condition of the chromatin, but as a rule the chromatin of 

 the young germinal vesicles appears as fine granules often very 

 evenly distributed throughout the nucleus as in Photos n, 14 

 and 1 7. Possibly this granular condition may be an artefact 

 one phase of a precipitate left after drying, for in some cases the 



1 Among recent observations on this point, Deton ('08) finds in Ihysanozoon 

 Brochii that the nucleolus is absent in the young oocyte, first appearing at the begin- 

 ning of the growth period. 



