RELATION OF GENES TO CHARACTERISTICS 1 89 



cell can produce many different parts of the organism. And 

 in many organisms even in late stages there are cells that 

 can produce any part, or the whole organism, as is shown 

 by the facts of regeneration. Such cells must contain the 

 entire set of genes. 



In very late stages of development it is possible that in 



Figure 42. Dividing cells of an early developmental stage of Ascaris 

 megalocephala, after Boveri (1910). The chromosomes in the two 

 large upper cells are broken into fragments, part of which are 

 dissolved and lost, while in the two lower cells the large chromo- 

 somes remain entire. 



highly differentiated tissue cells some or all of the genes 

 have become lost or modified, though there is no clear proof 

 of this. Further, there are a few organisms of which it is to 

 be observed that the cells that are to produce the differen- 

 tiated body of the animal lose parts of their chromosomes, 

 and so presumably some of the genes. The chromosomes in 

 these cells are seen to break up, and portions of them are 

 dissolved and absorbed by the cytoplasm (figure 42), while 



