HOLOTHURIA. 25 



while the predominant colour above was reddish-bro^vn. The suckers 

 are sometimes almost white, with a central red speck in their flattened 

 adhering extremities. The contracted tentacula of some are nearly 

 black. Perhaj)s it could be ascertained only by dissection, whether the 

 same internal parts are always lowest in position where the pale under 

 portion, if it be such, is applied to the sustaining substance. 



So many features enter the characters of what I would conceive the 

 Holothuria -pentactes, as certainly ought to facihtate recognition of the 

 species ; yet it seems to me, although I say it with reserve, that certain 

 discrepancies, apparently shght enough, among individuals, have prompted 

 naturalists to constitute two or three species of one : Nor is this the 

 only example of such an error, if it be an error, for the same has occur- 

 red of other Holothurioe. The whole subject, I repeat, is difficult ; yet 

 I fear that we create ambiguities Ijy neglectmg to shun them. 



No Holothuria is recovei'ed from the sea fit for immediate study. 

 All are disfigured or contracted ; some in one form, some in another. 

 Until relaxing into shape, adhering as a crescent, and displaying the 

 tentacula, nothing can be known of their nature. 



The skin of this species, the pentades, is very coriaceous, hard and 

 thick, tough, and difficult to be penetrated when in a contracted state. 

 It becomes as thin as pajier when the animal is distended, which is very 

 sensible in a specimen extending twelve or fifteen inches ; and it is more 

 evident in the higher and lower parts of one laid open. 



A very accomplished physiologist, Mr Henry Goadby, who had 

 devoted much attention to entomology, and the form of the invertebrate 

 animals, visited Edinburgh in 1841, where he gave some excellent lec- 

 tures in illustration of the preceding subject. At that time I happened 

 to be occupied with the Holothuria, and as he expressed a desire to see 

 that animal, with which he had never had the fortune to meet pre- 

 viously, I had the gratification of supplying him with several fine speci- 

 mens of the pcntades. 



Of these he made various preparations and dissections, far surpass- 

 ing any that has ever been seen, both for minuteness and beauty, in 

 shewing the form, the multipUcity, and the arrangement of the parts. 



