. The Biological bulletin. Biology; Zoology; Marine biology. 44 A. S. PEARSE. not again break up, as is the case in the arms of some ophuroids. Furthermore, if an individual is cut in two in the middle of the body the posterior half does not constrict off pieces, though it undergoes irregular contractions and constricted rings are often formed. The anterior half however will continue to fragment at its posterior end. The results are the same if an animal is cut in two in such a way that the posterior piece contains two thirds or three fourths of the body. cm s b. U I I I / ^â ^-
. The Biological bulletin. Biology; Zoology; Marine biology. 44 A. S. PEARSE. not again break up, as is the case in the arms of some ophuroids. Furthermore, if an individual is cut in two in the middle of the body the posterior half does not constrict off pieces, though it undergoes irregular contractions and constricted rings are often formed. The anterior half however will continue to fragment at its posterior end. The results are the same if an animal is cut in two in such a way that the posterior piece contains two thirds or three fourths of the body. cm s b. U I I I / ^â ^- i X I, Fig. 2. Thyone briareus. The right side of the body-wall as well as S'Tiie of the dorsal portion have been removed. The ampullse and mesenteries are not shown. b, point where body wall is ruptured in autotomy ; r, region where circular muscles are effective in preventing autotomy ; cc, cloac^l chamber ; ^ circular muscles ; CO., cloacal opening; ^, calcareous ring; ?', intestine ; in., integument; , longitudinal muscle bands ; , outer branch of longitudinal muscle bands ; , inner branch of longitudinal muscle bands ; , radial muscles which dilate the cloacal chamber ; , respiratory tree ; s, stomach ; t, tentacles ; x, weak point in inner branch of longitudinal muscle band. Thyone s mutilating reflexes always involve the loss of the nerve ring and the remaining portions of the body do not under- go further fragmentation but ultimately regenerate the lost parts. As in Leptosynapta there is no autotomy when the portion of the body which contains the nerve ring is absent. IV. Effect of Chemical Substances on Autotomy. In order to ascertain whether substances which increased the general excitability would induce a corresponding increase in the number of individuals manifesting autotomy, certain drugs and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readab
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