394 OSCAR RIDDLE. 



of this mass would probably make a reopening of the closed 

 channel very difficult or quite impossible. 



\Ve see then that the contraction of the contractile parts of 

 Tnbnlaria acts differentially upon its various organs. Such con- 

 traction does not rob the hydranth of its contained fluids, nor 

 of its ability to circulate these fluids. The same is true for the 

 stem region, except that there the actual movement of the fluid> i- 

 in abeyance for a very short time. The contraction which occurs 

 in the neck region, however, brings about far different relations 

 between the contracting area and the nutritive medium. Here 

 there results, not only a cessation of the circulation of fluids, but 

 a complete loss of contact with these fluids following the complete 

 closure of the channel; whilst finally the breaking of the dissepi- 

 ment immediately below the neck region, and the subsequent 

 plugging of the end of the connecting channel with pigment and 

 debris, preclude the possibility that such contracted region may 

 again regain its circulation together with the food it brings. This 

 area then necessarily disintegrates; and the break the autot- 

 omy necessarily occurs at this the weakest point. 



Our conclusion is that autotomy in Tubularia is the result of 

 the contraction of the animal; similar but weaker contractions 

 being common and central features in the behavior of the animal. 

 If the contraction be either too strong, or too much prolonged, 

 autotomy will follow. That is to say, if a very slight strain be 

 put upon the "neck" region while its circular fibers are in a state 

 of extreme contraction separation results at once. It the con- 

 traction be not so strong, but considerably prolonged, readjust- 

 ments are effected in the circulation which prevent the ingress of 

 food to the contracted "neck" region. Degeneration now occurs 

 in this region and the break the autotomy follows at this same 

 point. Then- is, then, no great mystery attached to "ramputa- 

 tion spontanee " ; not even a complex organic correlation to direct 

 a watchful and sacrificial neck in severing an offending head 

 from an unoffending body. 



The present work has been done at the Zoological Si.it ion at 

 Naples while occupying a table supplied by the Carnegie Institu- 

 tion of Washington. To the president of the Oirnrgir Institu- 

 tion, and to the director and assistants of the Zoological Station, 



