96 MORPHOLOGICAL DEVELOPMENT. 



eventually separates. Still more remarkable is the extent to 

 which this process is carried in certain kindred types ; which 

 exhibit to us several individuals thus being simultaneously 

 formed out of groups of segments. Fig. 169, copied (omit- 

 ting the appendages) from one contained in a memoir 

 by M. Milne-Edwards, represents six worms of different 

 ages in course of development : the terminal one being the 

 eldest, the one having the greatest number of segments, 

 and the one that will first detach itself; and the success- 

 ively anterior ones, with their successively smaller numbers 

 of segments, being successively less advanced towards fitness 

 for separation and independence. Here among groups of 

 segments we see repeated what in the previous cases occurs 

 with single segments. And then in other Annelids we find that 

 the string of segments arising by gemmation from a single 

 germ becomes a permanently united whole : the tendency to 

 any more complete fission than that which marks out the seg- 

 ments, being lost ; or, in other words, the integration having 

 become relatively complete. Leaving out of sight the 



question of alliance among the types above grouped together, 

 'that which it here concerns us to notice is, that longitudinal 

 gemmation does go on ; that it is displayed in that primitive 

 form in which the gemmae separate as soon as produced ; that 

 we have types in which such gemmae hang together in 

 groups of four, or in groups of eight and ten, from which 

 however the gemmae successively separate as individuals ; 

 that among higher types we have long strings of similarly- 

 formed gemmae which do not become individually independ- 

 ent, but separate into organized groups ; and that from 

 these we advance to forms in which all the gemmse remain 

 parts of a single individual. One other significant 



class of facts must be added. A few cases have been pointed 

 out, one of them quite recently, in which Annelids mul- 

 tiply by lateral gemmation. M. Pagenstecher alleges this 

 of the Exogone gemmifera : describing a certain number of 

 the segments of the body as severally bearing on their dorsal 



