CHAPTER VIII 



SELF-DIVISION AND REGENERATION. BUDDING AND REGEN- 

 ERATION. AUTOTOMY. THEORY OF AUTOTOMY 



SELF-DIVISION, as a means of propagation, is of widespread occur- 

 rence in the animal kingdom. In some cases the animal simply 

 breaks into pieces and subsequently regeneration takes place in the 

 same way as when the animal is cut into pieces by artificial means. 

 In other cases the parts are gradually separated, and during this 

 time new parts are formed by a process resembling that of regenera- 

 tion after separation. A few zoologists 'have tried to show how the 

 process cf regeneration before separation has been derived from 

 regeneration following self-division. It is our purpose to examine 

 here the evidence in favor of this hypothesis. 



A study of the forms that propagate by means of self-division 

 shows that the process is present in many groups of the animal 

 kingdom. In the unicellular forms this method is universally present ; 

 and in the multicellular forms the division of the individual cells is 

 looked upon as a process similar to the method of propagation in the 

 protozoa. The sponges do not multiply by self-division. In the 

 coelenterates, on the other hand, we find this mode of propagation 

 present in most forms. Hydra appears rarely, if at all, to divide by 

 a cross-division, and, although one or two cases of longitudinal 

 division have been described, it is not improbable that they have 

 been started by the accidental splitting of the oral end. The hydro- 

 medusae, Stomobrachium mirabile, Phialidium variabilc, Gastroblasta 

 Raffcelei, are known to increase by division. 1 Several actinians and 

 many corals divide longitudinally, while the scyphistoma of the 

 scyphomedusae produce free-swimming ephyras by cross-divisions 

 of the fixed strobila stage. The ctenophors do not divide. 



It is known that several fresh-water planarians propagate by 

 division, the tail-end breaking off in the region behind the old 

 pharynx. In one form, 2 and possibly in others, regeneration may 

 begin before the separation takes place. Many of the rhabdocoe- 

 lous planarians increase by cross-division the separation taking 

 place more nearly in the middle of the body. In these forms the 



1 See Lang ('88). 2 See Zacharias ('86). 



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