126 THE BIOLOGY OF THE SEA-SHORE 



regeneration from the cut surface so produced, while other 

 arms in the same specimen with the radial nerve intact 

 regenerate normally. 



The discussion of autotomy and regeneration in star- 

 fishes and brittle-stars affords a fitting opportunity to draw 

 attention to another important aspect of these phenomena. 

 This is the value of self-division as a means of propagation. 

 Among single-celled animals multiplication by division is a 

 perfectly normal phenomenon, and among the lower many- 

 celled animals it is also by no means uncommon. Anemones, 

 for instance, are capable of dividing lengthwise, and each 

 of the halves gives rise to a complete individual which 

 continues life on its own. 



One of the most remarkable of these cases of propagation 

 by self-division is found in Syllid worms. In this family 

 of marine worms, as we shall see in Chapter XII, the 

 hinder, genital portion of the body becomes separated 

 off from the anterior non-sexual portion. The sexual 

 portion then regenerates a new head, and the asexual portion 

 a new tail, which will, in due course, again become sexual 

 and split off once more. In the genus Autolytus the process 

 of separation is anticipated, as it were, by regeneration, and 

 as many as sixteen complete worms may be found as con- 

 nected links in a long chain. 



It is hardly possible to disregard these facts when 

 attempting to find an explanation of self- division in the 

 more special sense. Indeed, Morgan considers that the 

 process of autotomy differs from the process of self-division 

 as a means of propagation only in the fact that in autotomy 

 proper the part thrown off does not produce another animal. 

 Clark (191 3), again, in commenting on autotomy in the 

 starfish Linckia, states that this process affords an asexual 

 method of reproduction which is of prime importance. 

 Considerations of this kind serve to point to the possibility 

 of autotomy, in the strict sense, being rather of the nature 

 of a modification, for a special purpose, of the more funda- 

 mental habit of self-division as a means of multiplication. 

 This is a suggestion which is perhaps worth noting. 



