126 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



to bury itself will lead in a short time to violent contractions of 

 the posterior end of the body, resulting in the spasmodic contrac- 

 tion of the circular muscles at certain points with such violence 

 as to divide the body into two or more parts. The anterior part 

 may continue to cut off successive pieces until only a small frag- 

 ment of the anterior end of the body remains. This consists 

 of the tentacles, calcareous ring, nerve ring, and circular canal 

 of the water-vascular system, yet this fragment can under favor- 

 able conditions restore the normal proportions of the body. 



The posterior fragments, severed from the nerve ring, may 

 become much constricted but do not suffer further fragmenta- 

 tion. Such parts are unable to regenerate the whole body. 



In Thyone, the mutilation consists in such powerful contrac- 

 tions of the body muscles as to cause the rupture of the body 

 walls and longitudinal muscles immediately behind the calcareous 

 ring. This results in the ejection of the nerve ring, circular canal 

 of the water-vascular system, and a portion of the alimentary 

 canal, together with the whole crown of tentacles. Pearse* 

 describes a series of experiments to determine the conditions 

 under which such autotomy occurs. Various chemical stimuli and 

 foul water are the most effective agents in producing it. Such 

 mutilation as occurs in Thyone is doubtless entirely pathological 

 and probably causes the death of the animal in nearly all cases. 

 Pearse makes the statement, however, that regeneration of the 

 lost parts may ultimately occur. 



REGENERATION 



In their regenerative processes some of the holothurians 

 exhibit powers far beyond those of any other animals of such a 

 high degree of specialization. When disturbed, certain species 

 contract their bodies with such violence as to force out the greater 

 portion of their viscera, including not only the cloaca and res- 

 piratory apparatus, but also nearly the whole of the alimentary 

 canal. Under favorable conditions the normal body is restored. 

 While none of our own species have either this habit or its com- 

 pensating regenerative faculty, they are able to restore their 

 normal proportions after very considerable mutilation. 



* Biol. Bulletin, vol. xviii, pp. 42-49, 1909. 



