VEGETATIVE PROPAGATION 



329 



develop a disc and other arms, ultimately becoming a symmetrical 

 adult (fig. 854). 



Vegetative Propagation and Regeneration in Flat- Worms 

 [Platyhelntia). — 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 

 i^Microstomum /ineare) 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 {ChcEtopoda). — 

 The body of a worm of 

 this kind is made up of a 

 number of rings or 

 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 brouo-ht 

 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- 



Fig. 854. — Vegetative Propagation, 

 &c., ill 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 ntidtijlora)^ in which a new 

 disc and four arms are sprouting from 

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

 ijiultijlora) in which a new individual 

 is growing from a woundi^d arm. 



segments 



^'g- '855. — Fission- 

 Chain of Planarian 

 Worms {Microsto- 

 }n?{77z), reduced 



I, Original indivi- 

 dual. 2, 3, 3, New in- 

 dividuals, numbered 

 according to age. 



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 Brisde- 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 



Vol. III. 



84 



