35 6 W. E. HOY, JR. 



Deton, however, claim that eight and not four is the normal and 

 characteristic number. 



In Anglo stomum the chromosomes fragment in the cells of the 

 soma. The chromosomes of the sex cells are apparently bivalent. 

 The chromosomes of the somatic cells in Ascaris are derived 

 from a fragmentation of the compound chromosomes of the sex 

 cells. This fragmentation is accompanied by a "chromatin 

 diminution." 



Miss Stevens concluded in the case of Planaria that two inter- 

 breeding forms were present. The pairing of two individuals 

 with different chromosome numbers would explain, she writes, 

 the varying chromosome numbers she obtained. 



Wasserman and Gregoire have disputed the counts of Gold- 

 schmidt in Zoogonus. It may be that two different varieties 

 have been concerned, one with a chromosome complex of 10, 

 and the other with one of 12 or more. 



In considering the foregoing cases it is apparent that in general 

 the behavior of the chromosomes in the somatic cells can be 

 classified in the manner stated in the introduction to this paper, 

 namely that (i) the somatic and gonial chromosomes agree in 

 number and type, (2) the number of the chromosomes in the 

 somatic cells is higher than in the germ cells, due to a splitting 

 or fragmentation, (3) multiple chromosome groups are produced 

 by the suppression of a cell division, and (4) there is a synapsis, 

 more or less permanent, of all or certain pairs of chromosomes 

 in each cell generation. It is also evident that there are numerous 

 cases which are exceedingly perplexing, and which cannot be 

 classified at the present time. 



The majority of animals, particularly the insects, in which 

 group more work of a cytological nature has been done than 

 perhaps in any other, can be included in the first category. But 

 even here the classification is not sharp and distinct for many 

 forms may show at the same time the third type of chromosome 

 behavior in one or several tissues. This, however, does not 

 seriously affect the main conclusion, and is possibly to be con- 

 sidered as no more than a normal variation. 



When a sufficiently detailed study shall have been made of the 

 somatic chromosomes where some or all of these are represented 



