FORM-REGULATIONS IN CERIANTHUS. 2/5 



typical animal. From this piece tentacles regenerate at one end 

 and more or less growth of new tissue occurs at the other, but 

 neither of these is proportional to the size of the piece. It has 

 already been shown that the oral regeneration is too great in 

 amount to permit the reduction of the piece to the typical pro- 

 portions, but there remains the further question as to whether 

 the piece shows any approximation to typical proportion, or in 

 other words whether changes in proportion of the old parts 

 of the piece occur which can be interpreted as constituting an 

 approach to the typical form. 



In order to answer this question careful measurements of the 

 pieces repeated at frequent intervals are necessary, but measure- 

 ment is a difficult and uncertain matter in connection with Ceri- 

 antJius. The form varies so greatly with different degrees of dis- 

 tension and with the different activities of the animal that it is 

 impossible to obtain anything more than a rough approximation. 

 I have, however, carried out several series of measurements 

 extending over two months or more and have succeeded, I think, 

 in minimizing some of the sources of error. In making these 

 measurements various precautions were observed ; the pieces 

 were absolutely undisturbed for several hours, or in most cases 

 for nearly a day before the measurements were made, since it is 

 only in this way that anything like complete distension and 

 elongation can be obtained. Measurement was made by immers- 

 ing a small millimeter measure in the water with the specimen, 

 care being taken not to touch it, for a touch is likely to cause 

 instant contraction. All measurements were repeated several 

 times at intervals during the day, for there is no certainty that 

 the animal is fully distended at the time of a given measurement. 

 From these different measurements the maximum series was 

 selected as showing the largest size attained by the specimen 

 during a given day. The following dimensions were measured 

 for each piece so far as the parts designated were present ; the 

 whole length of the piece from disc to aboral pore ; the length 

 of the marginal tentacles ; the length of the labial tentacles ; the 

 length of the aboral outgrowth of new tissue ; if such were pres- 

 ent ; the diameter of the disc, i. e., the distance between bases of 

 tentacles on opposite sides ; the diameter about half way between 

 the disc and the middle of the piece, designated as oral diameter ; 



