134 GENERAL BIOLOGY 



individual is not budded off before another constric- 

 tion becomes visible, and the result is a chain of 

 individuals in various stages of differentiation. 



It is evident that if, instead of separating from the 

 parent organism, the newly formed " sub-individ- 

 uals " remain attached, we would have a resultant 

 organism of a different character, compounded, so 

 to speak, of individual units held together by a 

 sort of common bond. It is supposed by some 

 that the segmental structure more or less evident in 

 nearly all the animal kingdom came about originally 

 through some such suppressed fission. Just as we 

 have seen that whereas the stress of growth and the 

 necessity for maintaining a certain relation between 

 nucleus and cytoplasm results usually in the cleav- 

 age of the cell, but on the other hand results some- 

 times in the suppression of this cleavage through a 

 distribution of the nuclear substance to form multi- 

 nucleate cells or syncytia, so also conditions of 

 existence that in the beginning brought about a 

 cleavage of the whole organism (schizogeny) also 

 may have made it advantageous for the separate 

 parts to remain together. We can trace different 

 degrees in such a condition, from Ctenodrilus, in 

 which the separation is immediate, or Myrianida, 

 in which it is temporarily retarded, to the tape- 

 worm, in which the segments are permanently 

 attached together to form a " segmented body." 

 In the tape-worm, however, the segments at the 

 posterior end may drop off without losing such vital 

 functions as they are endowed with, and the number 



