REGENERATION, VARIATION AND CORRELA- 

 TION IN THYONE 



PROFESSOR JOHN W. SCOTT 

 University op Wyoming 



It is well known that many Echinoderms possess a re- 

 markable power of regeneration, and the results given 

 here show some interesting phases of this process in 

 Thy one briar ens (Leseur). The problem was suggested 

 a few years ago in connection with class work in the 

 Marine Biological Laboratory at Woods Hole, Massachu- 

 setts. There it is a common practise for students who are 

 taking the invertebrate course to keep aquaria in which are 

 placed specimens brought in from various collecting trips 

 in the vicinity. Students are encouraged to study the 

 behavior of these animals, but their enthusiasm for col- 

 lecting frequently causes them to overcrowd their aquaria, 

 with disastrous results. After collecting Thyone, espe- 

 cially if they are kept in stagnant water, the student is 

 frequently amazed to find one or more of his specimens 

 that have undergone evisceration. In this process the 

 animal not only loses the principal feeding organs, the 

 tentacles, and the entire digestive system, consisting of 

 the esophagus, stomach and intestine; but it also throws 

 out a whole series of organs surrounding the esophagus 

 including the circlet of calcareous plates, the nerve ring 

 forming the central nervous system, the portion of the 

 water- vascular system known as the ring canal with its 

 attached stone canal and Polian vesicles, and the muscles 

 which serve as retractors for the set of organs surround- 

 ing and attached to the esophagus. We shall refer to 

 these muscles as retractors of the esophagus. 



The remainder of the animal after evisceration con- 

 sists, principally, of the dermo-muscular integument, the 

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