DIMORPHISM IN SPERMATOZOA OF ANASA. 30 1 



spermatozoa grouped around the higher mode of the curve of 

 variability are those possessing the accessory chromosome, and 

 that those grouped around the lower mode lack this accessory 

 chromosome. The approximate equality of the two groups 

 (see Fig. 2), moreover, strengthens the view that the two groups 

 are produced as spermatids in equal numbers. 



However, some of the curves do not show this approximate 

 equality, but have marked digressions from a perfectly bilateral 

 symmetry. They may have been produced as spermatids in 

 equal numbers, and the departure from a bilateral grouping may 

 be due to a difference in nourishment; or this deviation may be 

 due to a slightly earlier ripening of the one group and their 

 ejection from the testis. 



Another interesting point brought out by the data is the 

 relation between the right and left testis of the same individual. 

 If the curves of ir and il, 2r and 2!, are examined carefully, they 

 are seen to approach bilateral symmetry even more closely when 

 right and left testes of the same individual are plotted together 

 than when each is plotted separately. Such combinations are 

 produced in Figs. 4 and 7. The former is the combination curve 

 for ir and il; the latter is the combination curve for 2r and 2!. 

 In the combination ir and il, of eight hundred individuals 

 plotted an actual difference of only eight is found between the 

 two sides, or a difference of only one per cent. In the combi- 

 nation 2r and 2!, a difference of only five exists between the two 

 sides of the curve, or a difference of only five eighths of one per 

 cent. On the other hand combination curves for the testes of 

 numbers 3 and 4 show no such close bilaterality. A probable 

 explanation for this discrepancy is offered in the relation between 

 the type of curve and abundance of spermatozoa. In the speci- 

 mens numbers I and 2 there was a great abundance of sper- 

 matozoa in each testis. Because four to five hundred individuals 

 were found to be reliable as a basis for a curve of variability, the 

 entire number was not measured, but random samples were 

 taken for measurement. In numbers 3 and 4, on the other hand, 

 a different condition existed. For each of these there were not 

 more than five hundred present in each testis. This abundance 

 or scarcity of spermatozoa may have a very vital connection 

 with the fundamental characters of the curve. 



