INDIVIDUATION AND REPRODUCTION 



211 



hydranth and another consisting of only the more apical portions 



(Fig. 8i). In still shorter pieces the proboscis with the sex organs, 



short tentacles, and mouth 



may appear in single or 



biaxial form without any 



vestiges of other parts (Figs. 



82, 83). And, finally, very 



short pieces give rise only to 



single biaxial apical portions 



of the proboscis with mouth 



and short tentacles (Figs. 



84, 8s). 



Whether the short pieces 

 produce single or biaxial 

 structures, it is at once evi- 

 dent that the more apical 

 regions of the tubularian 

 body, i.e., the hydranth, or 

 the apical regions of the 

 hydranth, can develop from 

 any piece of the stem quite 

 independently of the presence 

 of any other part of the body. 

 The conditions necessary for 

 the development of these 

 parts are present in each 

 piece, and the absence of 

 the stem or even the basal 

 portion of the hydranth 

 makes no essential difference 

 in the result. The occurrence 

 of the biaxial structures is as 

 a matter of fact an inci- 

 dental result of the shortness 

 of the pieces. In such pieces 

 the rate of metabohsm at 



75 



\^ 



Figs. 75, 76. — Ttibidaria: Fig. 7s, a single 

 individual; Fig. 76, reconstitution in a long 

 piece of stem. 



the two ends is often practically the same because they repre- 

 sent only a very small fraction of the whole axial gradient. 



