176 



MONTGOMERY A STUDY OF THE CHROMOSOMES 



together would correspond to the fifth bivalent chromosome of condition 1). To deter- 

 mine which of these conditions is the more usual, I counted the number of chromatin 

 elements seen on pole views of the monaster stage of the first maturation division. These 

 counts were made on spermatocytes from five different testes, and may be condensed into 

 the following table : 



Thus those spermatocytes with seven chromatin elements would seem to be the more 

 frequent condition. In both cases there is one univalent chromosome, which represents 

 the odd chromosome of the spermatogonia ; but why in cells of the second condition two 

 chromosomes should remain separated instead of combining to form a bivalent one, as they 

 do in the first condition, I cannot explain, unless perhaps the presence of the odd uni- 

 valent chromosome may in some way disturb the union into pairs of the ten other chro- 

 mosomes during the synapsis. 



In those cases where there are seven chromatin elements in the equator of the first 

 maturation spindle, the metakinesis results in the division of all the elements; this is a 

 reduction (transverse) division of the bivalent chromatin nucleolus and of the five bival- 

 ent chromosomes, but in what plane the univalent chromosome divides could not be de- 

 termined. Only one case was seen where the univalent chromosome was left undivided 

 in the equator after the daughter elements of the six other elements had reached opposite 

 poles of the spindle. Thus it would seem that in this division, in the cases where there 

 are seven elements present, all the elements become divided ; how it is in the cases where 

 there are eight elements could not be determined. In the spermatic! are found either six 

 chromosomes (Fig. 117) and one chromatin nucleolus (N. 2), or five chromosomes and 

 one chromatin nucleolus. This would show that the chromatin nucleolus and five chro- 

 mosomes (the derivatives of the original five bivalent ones) divide in the second matura- 

 tion division, but that the sixth chromosome, the derivative of the originally univalent 

 one, does not divide but passes undivided into 'one of the two spermatids. Thus the 

 valence of the seven elements in these generations would be : first spermatocyte, one 

 bivalent chromatin nucleolus, five bivalent chromosomes, one univalent chromosome ; 



