CHROMOSOMES OF ACHOLLA MULTISPINOSA. 1 79 



the present case of Acholla giving the greatest variation in num- 

 ber. In fact so many variations have been ffound that we may 

 justly ask what is to be the Hmit of these irregularities and where 

 will they lead us ? 



The case of Acholla is interesting for two principal reasons. 

 First, it gives us the greatest variation in number so far discovered, 

 there being a difference of four between the male and female 

 groups. Secondly, if we examine the size relations carefully it 

 will be noticed that the large chromosome which goes to the 

 male-producing pole seems to contain a larger amount of chro- 

 matin than the five chromosomes of the hexad group which go 

 to the female-producing pole. A number of measurements show 

 this to be the case. In all the irregularities hitherto described, 

 the female cells contain the larger number of chromosomes and 

 also the greater quantity of chromatin. The present case is not 

 an exception to the number but seems to be in regard to the 

 quantitative relations. 



Several recent theories of sex determination have been based 

 upon the quantitative relation of the chromatin. The evidence 

 in Acholla forms one of the stumbling blocks in the way of some 

 of 'these interpretations. To be sure, if we should ignore the large 

 chromosome, the homologue of the small idiochromosome, or 

 what Wilson terms the Y element, many difficulties would dis- 

 appear. Most certainly though, as Morgan says, there is no 

 reason for disregarding it except that its presence, in an active 

 condition, does not fit in with our hypothesis. In his recent 

 paper on " Sex Determination in Phylloxerans and Aphids," 

 Morgan while realizing the difficulties in its way, further develops 

 the quantitative hypothesis and holds to it as a rough approxima- 

 tion to a solution. In regard to the case of Acholla he suggests 

 that possibly the five chromosomes of the hexad group which go 

 to the female-producing pole are more active than the large 

 chromosome which goes to the male-producing pole. The sug- 

 gestion may be true, but is the question of the activity of the 

 chromosomes the same as that of the quantitative relations ? 



