MARY T. HARM AN AND FRANK P. ROOT. 



Most of the cells in the actively dividing stages of our material 

 are diagrammatically clear. Owing to the fact that some of 

 the chromosomes are precocious and others are lagging, many of 

 the polar views of metaphase plates do not contain all the 

 chromosomes. 



It is of some interest to note that although there is a great 

 difference in the number of chromosomes reported for the guinea 

 pig, no one has reported an unpaired chromosome and only 

 Stevens (1911) has previously reported one which divides un- 

 equally. This is the condition which Painter (1923 and 1924) 

 has found for the opossum, two species of monkeys, the horse 

 and both the negro and the white man. However, it differs from 

 the findings of Wodsedalek (1914) and Masui (1919) for the 

 horse. Since the female has not been studied the basis for 

 calling this pair of unequally dividing chromosomes the XY-pair 

 is the behavior. \Ve have chosen to call the large component 

 the X-element and the smaller component the V-element because 

 this is the condition in those animals in which the homologues 

 have been studied in the female. It is perfectly possible that 

 an examination of the female might reveal the opposite condition. 

 This is of further interest because it is cytological evidence that 

 the male guinea pig is heterozygous for sex which has been taken 

 for granted among geneticists but which has not been shown 

 experimentally. Known sex-linked characters in the mammals 

 are few. They have been found in man and the cat. 



\Ye have found no indication of telosynapsis as was described 

 by Moore and Walker (1906). They state that "In the guinea 

 pig there are, as we have seen, 32 prernaiotic chromosomes, and 

 the synaptic loops of the first maiotic division resolved them- 

 selves into 1 6 gemini, so that we are led to conclude that gemini 

 consist each of two somatic chromosomes joined end to end." 

 Neither have we found a condition which could certainly be 

 interpreted as parasynapsis. The condition illustrated in Fig. 3 

 might be interpreted as parasynapsis, but could as readily be 

 considered as a precocious splitting of the chromosomes in tetrad 

 formation. The fact that there are four U-shaped primary 

 spermatocyte chromosomes and that there are eight similar 

 shaped spermatogonial chromosomes would be evidence in favor 



