VEGETATIVE PROPAGATION 



3 2 9 



develop a disc and other arms, ultimately becoming a symmetrical 

 adult (fig. 854). 



Vegetative Propagation and Regeneration in Flat- Worms 

 (Platyhelmia). The members of this group are commonly able 

 to repair injuries and re-grow lost parts with facility. As we 

 shall see in a subsequent section, vegetative propagation plays 

 an important part in the life-histories of such parasites as Flukes 

 and Tape- Worms, and it will perhaps suffice for our present pur- 

 pose to mention the transverse fission which regularly takes place 

 in certain Planarian Worms (Turbellaria). A 

 typical case is presented by a freshwater form 

 (Microstomum lineare] depicted in fig. 855, and in 



which a temporary chain of 

 individuals results from suc- 

 cessive divisions. 



Vegetative Propagation 

 and Regeneration in Bris- 

 tle - Worms ( Chcetopodd). 

 The body of a worm of 

 this kind is made up of a 

 varying number of rings or 

 segments which, broadly 

 speaking, resemble one an- 

 other in structure. And 

 supposing some of these 

 rings to be accidentally cut 

 off, or to fall a prey to some 

 predaceous animal, the life of the worm is not thereby brought 

 to an abrupt conclusion, for the injuries are speedily repaired. It 

 has been suggested, with some show of probability, that segmen- 

 tation of the body has been evolved as a protective measure (see 

 vol. ii, p. 375), but this is rather doubtful, for unsegmented worms, 

 such as Planarians, are also distinguished by great powers of re- 

 generation. 



It is not surprising to find ability to replace lost parts asso- 

 ciated in some cases with vegetative propagation. This is the 

 case in one of the marine Bristle -Worms already mentioned 

 (p. 318), and the process essentially consists in the rapid growth 

 or budding-out of the region immediately in front of the posterior 

 end of the body. A transverse division is next effected, renewed 



Fig. 854. Vegetative Propagation, 

 &c., in Star-Fishes, reduced 



A, A Star-Fish (Ophidiaster diplax], 

 in which two arms (i, 2) are about to be 

 pinched off, and three others (3, 4, 5) 

 re-grown. B, A "Comet" Star- Fish 

 (Linckia multiJJora), in which a new 

 disc and four arms are sprouting from 

 a detached arm. c, A Star-Fish (L. 

 multiJJora) in which a new individual 

 is growing from a wounded arm. 



Fig. '855. Fission- 

 Chain of Planarian 

 Worms (Microsto- 

 mum}, reduced 



i, Original indivi- 

 dual. 2, 3, 3, New in- 

 dividuals, numbered 

 according to age. 



VOL. III. 



84 



