162 QUARTERLY CHRONICLE. 



Ocnus, &c.), which recall the cutaneous skeleton of the 

 Echinids. Either the " stools " or the connective corpuscles 

 may sometimes be entirely deficient. However, the case 

 where calcareous corpuscles of all forms are absolutely 

 wanting are very rare (in certain types of the family of the 

 Synaptids and of the Molpadids). 



It is well known that all the Holothuriae are characterised 

 by the presence of a ring composed of calcareous pieces dis- 

 posed round the pharynx; a ring which one might, perhaps, 

 consider as the homologue of the lantern of Aristotle in the 

 Echini. This organ is formed, as a rule, by ten pieces, of 

 which five are radial and five interradial, the former each 

 pierced by an opening for the passage of the aquiferous 

 ambulacral vessel. M. Semper cites a case, that of a 

 Pentacta from Japan, in which the interambidacral pieces 

 are entirely absent, and the ambulacral pieces are reduced 

 to little calcareous plates, lodged in the skin of the pharynx. 

 M. Semper distinguishes two forms of ambulacral appendices : 

 the ambulacral feet , furnished at the extremity with a sucker 

 strengthened by a calcareous plate ; and ambulaci'al papillce, 

 which are conical and pointed. The first belong, as a rule, 

 to the ventral trivium ; the second to the dorsal bivium. 

 However, in certain cases, one can find ambulacral feet on 

 the back, and also ambulacral papillae on the belly — excep- 

 tions which are both realised together in the genus Sporadipus. 

 As is known, ambulacral appendices are totally wanting on 

 the back of the Dendrochirotids. Among the Molpalids 

 these appendages are absent throughout, though the branches 

 corresponding to the five ambulacral vessels do not the less 

 pierce the skin. Lastly, in the Synaptids of the tropics, the 

 author establishes the complete absence of the five ambulacral 

 vessels, which M. Baur had already done for the European 

 Synaptse. 



The organs of Cuvier sometimes are attached directly to 

 the cloaca, sometimes to the stem of the lungs. The author 

 confirms afresh the view that they are not hollow, but solid, 

 and he contests their glandular nature. He considers them 

 as a sort of weapon that the animal can j^ush out behind by 

 the cloaca! It is true that this phenomenon is always accom- 

 panied, like the projection of the viscera so peculiar to the 

 Holothuriae, by the rupture of the wall of the cloaca. 



Among many Holothuriae (Aspidochirotids) the dorsal 

 vessel is broken up in the intestinal looj:) into a rcte mirabile, 

 which becomes entangled with the ramifications of the left 

 lung. Johannes Miiller admitted that this entanglement 

 does not constitute bv anv means a close union of the two 



