HOLOTHURIAD^E. 



199 



in others very few, and unite to form a tube which opens 

 at one side towards the upper extremity of the animal. 

 The inner surface of the animal's skin is lined with power- 

 ful longitudinal and transverse muscles, by means of which 

 the creature contracts its body and lengthens it out in 

 many directions, changing its form in a wonderful man- 

 ner. Sometimes the creature ejects all its viscera, or 

 bursts the body with its convulsive contractions. It is 

 usually stated that the ffolothurice do so whenever they 

 are taken, but such is not the case. I have never seen 

 the animal disgorge its intestines, but specimens of many 

 species have I seen in which there was not a trace left of 

 the creature's bowels and other internal organs, though it 

 seemed when taken alive and healthy. It is astonishing 

 how long they can live deprived of the most essential parts 

 of their organism. Sometimes they are found wanting 

 the respiratory organs, and sometimes the generative tubes 

 are deficient, and these deficiencies so frequently occur that 

 we should be extremely shy of proclaiming differences in 

 the internal structure of species ; and when we see genera 

 and species (as has been the case) anatomically defined 

 from the want of respiratory trees or genital tubes, we 

 should be extremely cautious about admitting such, and 

 rather regard such wants as accidental deficiencies in a 

 few specimens than as organic peculiarities. 



Sir John Graham Dalyell, whose knowledge of the habits 

 of the lower invertebrate animals exceeds that of any living 

 naturalist, communicated some most interesting observa- 

 tions on reproduction of organs in the Holothurise, to the 

 meeting of the British Association at Glasgow in 1840. He 

 there stated that he had observed them lose " the tentacula, 

 with the cylinder (dental apparatus), mouth, oesophagus, 

 lower intestinal parts, and the ovarium, separating from 



