458 E. ELEANOR CAROTHERS 



which in the preceding animals has been heteromorphic has both 

 homologues of the atelomitic type. If we study individual 

 number 6 we find that it has no J-shaped tetrads; it has eight 

 atelomitic and only three telomitic tetrads. Comparing indi- 

 viduals 6 and 7 it is seen that chromosomes number 9 to 6 

 inclusive are atelomitic in the former and J-shaped in the latter. 



It is also interesting to compare more in detail individuals 

 number 2 and number 6. Chromosome number 1 in individual 

 number 6 is the type which would be expected to result if the 

 spermatozoon carrying the V-shaped dyad of this chromosome 

 in animal number 2, for instance, united with an egg bearing a 

 similarly shaped dyad. The shape of chromosomes number 6 

 and number 8 of animal number 6 may be accounted for on a 

 similar assumption. Conversely we would expect to find, then, 

 in some individual the two telomitic homologues of these two 

 tetrads, and this is exactly what we have in animal number 2. 



Clearly, then, the complex is not constant in this species, ac- 

 cording to our past conceptions of constancy as indicated by 

 form of chromosome, since a given chromosome in one member 

 of this species may be of the Stenobothrus type, in another of the 

 Hippiscus type, while in a third, one homologue of this same 

 chromosome is of the Stenobothrus type and the other of the 

 Hippiscus type. This is most easily demonstrated by following 

 chromosome number 1 through several plates. Taking plates 

 2 and 3 we find this element of the mixed type in eight of the six- 

 teen individuals, while it is of the Stenobothrus type in four and 

 of the Hippiscus type in four. For the entire sixty-two individ- 

 uals under consideration this tetrad is of the Stenobothrus type 

 thirteen times, Hippiscus type eighteen times, one homologue 

 of each type thirty-one times. This comes very close to the 

 1-2-1 ratio that we might expect on Mendelian principles if the 

 two types occur with equal frequency in nature and chance fer- 

 tilization occurs. 



The next point was to determine, so far as my material per- 

 mitted, the range of variation. I wish to emphasize the state* 

 ment previously made that the arrangement in the plates ac- 



