HOLOTHURIA. 47 



what enlarged in trumpet shape ; and that the intermediate portion is a 

 muricate or tuberculate cylinder. Possibly subordinate organization 

 might be discovered in the flattened disc ; but the opportunities of bring- 

 ing any part of the organ whatever under the microscope are so rare, as 

 to prove a great obstacle to inspection. Were there any question of 

 their solidity, they might be supposed absorbents, for the peculiar or- 

 ganization employed in this function is not obvious, — it goes on however 

 to a great extent. Sometimes the flattened disc seemed reddish during 

 observation, and conjectures were entertained of the motion of globules 

 or a fluid in the cylindrical part. But the illusions concomitant on arti- 

 ficial aid are so ready to disturb the truth, that the naturahst distrusting 

 himself cannot repeat his observations too carefully, or too often, before 

 arriving at definite conclusions. The microscope demands many pre- 

 cautions. Besides the numerous suckers anchoring the subject to the 

 sides of its vessel, many free and disengaged stretch around in various 

 directions, as if in search of other objects. Several days frequently 

 elapse before weaker specimens affix themselves, therefore some exertion 

 seems requisite. 



The animal being secured by adhesion of the suckers, its position is 

 seldom changed afterwards. Curvature of the crescent may augment or 

 diminish while adhering ; and adhesion ceasing, progression may ensue. 

 For a long time I was much perplexed as to the mode wherein this was 

 accomphshed. I could not form an opinion regarding the advance of 

 the one or the other extremity. From certain indications, and especially 

 from the madequacy of the arborescent apparatus to encounter resist- 

 ance, I rather concluded that it must be the opposite extremity ; and 

 this fact was apparently corroborated by the timidity of the animal, and 

 its singular care to protect the tentacula. But I was mistaken : the 

 Holothuria, as most natural to believe, advances head foremost, — and 

 with the arborescence displayed. Commencing progression, the suckers 

 in front are relaxed, while those free behind are brought forward and 

 secured ; the former fix again, and the latter being loosened, the body is 

 advanced. Thus are steps effected, and the transition of the Holothuria 



