Vol. XVI. April, /pop. No. 5. 



BIOLOGICAL BULLETIN 



THE NUCLEOLI IN THE SPERMATOCYTES AND 



GERMINAL VESICLES OF EUSCHISTUS 



VARIOLARIUS. 



TvATHARINE FOOT AND E. C. STROBELL. 



I. In the resting first spermatocyte of many insects there 

 appears a spherical, chromatic body which invariably stains as 

 intensely as the chromosomes. 



McClung ('02) was the first investigator to draw special 

 attention to this structure by his suggestion that it may function 

 as a sex determinant. 



A majority of the cytologists who have studied this structure 

 interpret it as one of the chromosomes which persists through 

 the rest stage of the first spermatocyte, and they claim that its 

 presence or absence in a spermatozoon is the determining factor 

 of sex, McClung assuming that its presence in a spermatozoon 

 causes the fertilized egg to produce a male, whereas Stevens, 

 Wilson and others affirm that its presence in a spermatozoon 

 causes the fertilized egg to produce a female, and in those cases 

 where two (a large and a small) chromatin nucleoli are present, 

 the larger is the female-determining, and the smaller, the male- 

 determining factor. 



Identifying the chromatin nucleolus as a chromosome enlarges 

 at once the sphere of the problem, involving this structure in the 

 maze of hypotheses and theories associated with the chromosomes. 

 This identification of the chromatin nucleolus as a chromosome 

 is of great importance, because it presumably demonstrates that 

 a definite chromosome retains its individuality throughout the 

 rest stage, and it presents very strong evidence for the theory 

 of the individuality and continuity of the chromosomes-- the 

 theory which is the corner-stone of all hypotheses involving the 



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