284 C. M. CHILD. 



According to this view the elongation of pieces of Cerianthus 

 and the extremely elengated form of the body of normal animals 

 are due to the same factors. 



The tubicolous habit of the animal may perhaps be regarded 

 by some as responsible in some degree for its elongated form. 

 In the tube only longitudinal increase in size can occur. The 

 animal frequently leaves its tube, however, and burrows in an- 

 other spot ; the size of the new tube will be determined by the 

 size of the animal in each case. Moreover, I do not think the 

 reduction in transverse diameter observed in pieces can be ex- 

 plained in this manner. The slime which encloses the bodies of 

 specimens kept in clear water is not sufficiently elastic to reduce 

 the diameter. In so far as the burrowing tubicolous habit is cor- 

 related with the creeping habit, it may constitute a factor in the 

 production of the characteristic elongated form. 



One point still requires brief consideration. The table and the 

 figures indicate that piece C undergoes a much greater change of 

 form than the other pieces. It is the only piece in which the 

 length of the old part is greater at the end of the experiment than 

 at the beginning, /. e., provided the measurements are correct. 

 There is of course uncertainty regarding all the measurements 

 but if we suppose this difference between 7 and the other pieces 

 to be real it requires explanation. 



In my study of Stenostoma (Child, '02, '03) it was shown that 

 the change in direction of the tension upon the tissues is an 

 important factor in change of form. In a short piece of 

 Stenostoma using its posterior end as an organ of attachment the 

 directions of the various strains to which the tissues are subjected 

 differs much more from those to which they were subjected as a 

 part of the whole than would be the case in a long piece. This 

 must be true in all cases except where the posterior end of the 

 piece formed the posterior end of the whole. In that case the 

 directions of the strains remain as before. For further considera- 

 tion of the case the reader is referred to the above-mentioned 

 paper. The point of importance for our present purpose is that 

 the short piece must undergo greater change of form than the 

 large piece except when it is taken from the posterior end. 



We can I think, apply the same course of reasoning to Ceri- 



