MULTIPLE CHROMOSOMES 561 



for producing all the chromosomal arrangements found in H. 

 viridis is at hand. Thus a two rod spermatozoon and a two rod 

 egg would produce a complex having chromosomes 9 and 10 

 free as in classes 1 and 6. A double-V spermatozoon and a 

 two rod egg would bring about the condition shown in class 4 

 where these chromosomes are joined at one end, while such a 

 spermatozoon, united with an egg of similar composition, would 

 result in the complete ring of class 5. It seems evident there- 

 fore that the forms of chromosomes found in the male germ cells 

 may be accounted for on the basis of persistent fusions, segre- 

 gations and recombinations. 



Similarly, if chromosomes 11 and 12 are compared, we find the 

 two rod, incomplete ring, and ring, and the argument for their 

 relation is the same as for the preceding case. There are how- 

 ever two notable differences between the series. Of the six 

 classes, only two show multiples of chromosomes 9 and 10, while 

 four classes have combinations between 41 and 12. Again, the 

 incomplete ring is as frequent as the complete in classes 4 and 

 5, while only one individual out of twenty-six belonging to classes 

 3 to 6 failed to have a union of the two tetrads at both ends. 

 Thus we learn that the tendency of the large elements to unite 

 is more pronounced and complete. In this connection it may 

 be noted that in class 2 the largest element, although failing to 

 form a union with a euchromosome, is united to the accessory 

 chromosome. Only four individuals of the thirty-seven show this 

 element not joined to another chromosome. Of similar import 

 is the combination between the accessory with the largest free 

 euchromosome in class 4. It is possible that the largest free 

 tetrad is involved in class 3, although I judged it to be next to 

 the largest when the drawing was made. Another thing to be 

 noted is that only tetrads of nearly equal size unite together. 

 The accessory chromosome is never joined to a chromosome of 

 lesser size. 



The form of the multiples, as represented on the tabular 

 series of plate 2, is the one best adapted to serve as a means of 

 comparison between them and the free chromosomes of other in- 

 dividuals. This relatively simple configuration is, however, not 



