THE MORPHOLOGICAL COMPOSITION OF ANIMALS. 101 



form while still in the egg. But it does this in just the 

 same manner as before. Indeed, the essential identity of the 

 two modes of development is shown by the fact that the seg- 

 mentation within the egg is only partially carried out: in 



765 



all these types the segments continue to increase in number 

 for some time after hatching. Now this process is as 



like that by which compound animals in general are formed, 

 as the different conditions of the case permit. When new 

 individuals are budded-out laterally, their unfolding is not 

 hindered — there is nothing to disguise either the process or 

 the product. But gemmae produced one from another in the 

 same straight line, and remaining connected, restrict one 

 another's developments; and that the resulting segments are 

 so many gemmiparously-produced individuals, is necessarily 

 less obvious. 



§ 206. Evidence remains wdiich adds very greatly to the 

 weight of that already assigned. Thus far we have studied 

 only the individual segmented animal ; considering what may 

 be inferred from its mode of evolution and final organization. 

 We have now to study segmented animals in general. Com- 

 parison of different groups of them and of kinds within each 

 group, will disclose various phases of progressive integration 

 of the nature to be anticipated. 



Among the simpler Platyhelminthes, as in some kinds of 

 Planaria, transverse fission occurs. A portion of a Planaria 

 separated by spontaneous constriction, becomes an inde- 



