Cuvierian Organs o/IIolotlmria nigra. 277 



pvessuve of fluid from the cloaca ; but that is certainly not 

 the case in Holothuria nigra. In tliis form the organs elon- 

 gate entirely of themselves in response to stimuli, which may 

 be applied to the organs themselves or to the ])eripheral 

 sense-organs of the animal, which is the normal process. 

 Moreover, when once the organ has elongated it cannot be 

 again retracted, but is cast off, a constant supply of such 

 organs being kept up by outgrowths from the respiratory 

 tree. Examination of isolated organs shows that the elonga- 

 tion and the formation of the sticky thread commence at the 

 base, and that the ''head" wliich rushes about so. wildly in 

 the water is the remains of the original Cuvierian organ. In 

 normal healthy cases the head becomes entirely used up in 

 the formation of the sticky thread ; but often its power 

 slackens and stops while a great deal is still unused. As tlie 

 energy gets less the thread produced is not straight, but 

 wavy, as in fig. 1 b. This can well be seen by putting the 

 organs in corrosive sublimate or Kleinenberg's picric, when 

 the wavy appearance is produced as the reagent gradually 

 overcomes the power of elongation. 



To resume, the following appears to be the normal process. 

 Irritation of the skin of tlie Holothurian is transmitted ulti- 

 mately, along what nerve-paths I cannot say, to the base of 

 Cuvierian organs. Certain of these commence to elon«:ate 

 with great rapidity, in what way is not clear — most probably 

 as described by Jourdan, but certainly not as the result of 

 pressure of fluid. As a result they soon find their way out 

 of the body and continue to elongate outside, being generally 

 directed by the animal, so that some of the tubes are almost 

 certain to come in contact with, and stick to, the irritating- 

 body or foe. After this they break off at their point of 

 attachment to the respiratory tree, and new organs grow to 

 replace them. 



The next point to examine is the 



"d. Ejection of the Cuvierian Organs. — The problem here 

 may be briefly stated as follows. The Cuvierian organs are 

 attached to the respiratory tree and lie entirely in the body- 

 cavity, with their free ends pointing- away from the anus. 

 When ejected they emerge from the anus with the free end 

 foremost. To do this it is obvious they must in some way 

 pass through the wall of the gut. 



According to Semper (7) they come through an opening in 

 the wall of the cloaca with their free end foremost. It is left 

 an open question Avhether the opening they pass through is pre- 

 formed or arises by dehiscence at the time the organs are thrown 

 out. Luduig (5, p. 401) considers that our anatomical knowledge 



