278 Mr. E. A. Mincliin on the 



points to the latter view. Il(5roiiard seems to agree with 

 Semper, for he states tliat the whole process is the first act 

 of expulsion of the digestive tract, and that when the wall of 

 the cloaca is torn the Cuvieriaii organs, being nearest to it, 

 are thrown out. 



On the other hand, Cuenot (2, p. 371) has a more compli- 

 cated tlieory. He says : — " As H(^rouard has shown, the 

 water enclosed in the cloaca penetrates into the basilar vesicles 

 [which in Holothuria nigra do not exist], and from thence 

 gradually into the tubes, which dilate little by little, this 

 dilatation coinciding with the contraction of the irritated 

 animal. The ])ressure in the interior of tlie body increases ; 

 the tubes tend to be rejected to the exterior; at this moment, 

 it is a point which escapes direct observation, tiiey break at 

 their base of insertion on the basilar vesicle, which presents 

 probably a locus minoris rrsistsntice, pass through it and the 

 cloaca, and are rejected by tlie anal orifice. The basilar 

 vesicle then contracts, the strong muscular walls apply them- 

 selves to one another, so interrupting all communication 

 between the coelome and the exterior." 



, If I have understood this description properly I gather 

 that the Cuvierian organs break off completely at their bases 

 of insertion and then pass bodily through the hole thus made. 

 I further infer from it that the Cuvierian organs should 

 emerge with their bases foremost. All these statements arc 

 negatived by the facts observed in Holuthuria nigra. The 

 organs do not emerge with their bases foremost and they do 

 not break off from their attachment until they have spent 

 themselves and are firmly fixed to some object, when they are 

 violently broken away from their attachments to the respi- 

 ratory tree by the animal's movements. 



1 have had many opportunities of studying the method in 

 which tliese organs arc rejected, and can completely confirm 

 Semper's account. While opening Holothurians to obtain 

 gregarines a great number of Cuvierian organs were always 

 ejected by them, and in such specimens an aperture in the 

 dorsal wall of the cloaca could always be found, and very 

 often Cuvierian organs would be found in the aperture. 

 After many attempts I was able to make and draw the dissec- 

 tion shown in Plate XVll. fig. 9, in the following manner: — A 

 fresh Holothurian being obtained, it was placed on a sheet of 

 cork and made to eject some Cuvierian organs. Then with 

 a sharp knife the body was opened on the riglit side by a 

 ■ longitudinal cut and the integument pinned out right and 

 left. Weak spirit was then poured on to the surface of the 

 water, in order to subdue the action of the powerful body- 



