XIH] MICROSOMES 205 



survive. BRACKET ascribes this non-viability to incompati- 

 bility between the tissues arising from such different cells, 

 and if this is so in the frog, some similar condition may 

 perhaps also exist in those parts of the disp.ermic Echinoid 

 larva which fail to develop normally. 



In conclusion, although all the four groups of arguments 

 given above in favour of the individuality theory refer to 

 the chromosomes as complete entities, it is important to 

 remember that they are in all probability divisible into 

 smaller units, and that these units, supposed to be arranged 

 in a definite order along the length of a chromosome, prob- 

 ably have an individuality more fundamental than the 

 chromosome as a whole. That this is so is strongly suggested 

 by such cases as that of Ascaris, and is a necessary assump- 

 tion for the hypotheses regarding the function of the chro- 

 mosomes in heredity that will be considered in the next 

 chapter. Not infrequently, especially in the spireme stage 

 of the nucleus, the chromosomes can be seen to be made up 

 of a series of granules, like beads on a string, and with the 

 support of instances like the compound chromosomes of the 

 germ-track of Ascaris,\t seems a not unreasonable extension 

 of the individuality theory to regard these granules ("micro- 

 somes ") as the fundamental units, and to modify the theory 

 in the way suggested in the introductory portion of this 

 chapter. 



