390 OSCAR RIDDLE. 



adequate cause of autotomy. I therefore gave a little speci.il 

 attention to this subject, the results of which may be summarized 

 here. 



The particular experience which seemed to contravene the 

 proposed causes as being tin- actual immediate cau>e \vas the 

 following: If normal healthy indi\ iduak of T. mesembryanthemum 

 be held by the lower stem or stolon and drawn through any one 

 of a variety of solutions sodium tellurite, sodium selenite, etc. 

 complete autotomy may occur in less than one minute! Clearly 

 degeneration is not the cause of the autotomy in these cases. 

 Other members of the colony taken from their moorings and 

 placed in vessels supplied with fresh sea water remained for 

 days without autotomy. When some of these wen- similarly 

 drawn through pure sea water they remained intact without 

 autotomy. It was found, moreover, that the autotomy likewise 

 occurred even when the animal was dipped into a solution of 

 NaoTeOa, NaSeO 3 , etc., of lower temperature than that from 

 which it had just been removed. Here, too, the autotomy was 

 rapidly and decisively effected. In these cases the autotomy 

 plainly could not have been caused by a rise in temperature; the 

 temperature change actually being in the opposite direction. In 

 many cases the animals were removed from water at 16 C. 

 and drawn through a solution at 13 C. 



In order to study the changes occurring in the rapidly air 

 totomizing animals these were examined with a Zeis^ binocular 

 while being drawn through the solutions. By this means it was 

 found: (i) that as soon as the animal touches the solution there 

 follows a very strong contraction of tentacles, hypostome, peri- 

 stome, etc.; (2) that the "neck" region becomes extremely con- 

 tracted and narrow, and apparently so much weakened as to be 

 unable longer to support the weight of the hydranth; or rat la r 

 too weak to sustain the slight pull on the hydranth as it is being 

 drawn through or lifted from the solution. The appearance hen- 

 is such as to indicate that the contraction of the circular libers 

 of this region is of sufficient force, not only to close completely 

 the central channel, but also to separate and cn\\d out. many 

 entodcrm cells, and likewise to weaken their o\\ u adhe>i<>ii and 

 that of the other ectoderm cells to each other. .1 ri^onms con- 



