146 Descriptions of Preparations. 



disposed than those of the two rays of the dorsally placed bivium ; 

 and of the ten tentacles the two which are placed immediately 

 opposite the central ray of the dorsal trivium, and one of which 

 is placed therefore on either side of the medio-ventral line, are very 

 much smaller than any of the other eig-hf*. The ventral trivium 

 gives the surface of the body which it occupies a somewhat flatter 

 surface than is possessed by the surface corresponding* to the dorsal 

 bivium ; and this, tog-ether with the diminution in number and 

 importance of those two rows of ambulacra, appear to constitute 

 a transitional arrangement between the more perfectly pentagonal 

 appearance which nearly allied species may present, and the close 

 adumbration of the form of an ordinary Gasteropod which we note 

 in Psolus (Cuvieria), where the dorsal bivium is wholly aborted. 

 The ten tentacles are seen to be carried upon the outer rim of a 

 eylindriform prolongation of the body-walls, which is transparent 

 and carries no ambulacral feet. The anti-ambulacral surface is 

 reduced in Holothurioidea as it is in Echinoidea to the small region 

 immediately surrounding the anus ; in Cucmnaria communis, indeed, 

 the ambulacra almost abut upon that orifice ; and it may be here 



f" Systematic zoologists differ as to whether the smaller size of the pair of ambu- 

 lacral tentacles, which are placed opposita the central ray of the ventral bivium, 

 is of generic, of specific, or even of less classificatory importance. Troschel, in the 

 Archiv. fur Naturgeschichte for 1846, speaks of this difference as being of generic 

 value, and as separating Cladodactyla {Cucumaria) doliolam, Brandt ; Cladodactyla 

 Dicquemarii, Cuvier and Brandt^ and Cladodactyla Syracnsana from the species 

 here described. Forbes, however, in his 'History of British Star-fishes,' 1841, says 

 of Cucumaria pentactes, ' It is extremely variable in colour ; generally of a deep 

 purple, sometimes altogether white, sometimes pui-plish white. The tentacula and 

 head of both varieties vary equally, either purple or white. It varies also in the 

 pinnation of the tentacula, and in their relative size and number. The Holothuria 

 Montagui of Dr. Fleming, founded on a white variety described by Montagu, 

 has tight full-sized tentacula and two small ones, which are alternately in motion 

 covering the mouth. The tentacula of this form are not so pinnate as in the 

 common or purple state.' It has been said that the ' Cuvierian organs,' certain 

 structures of various forms and doubtful function attached to the stem of the 

 respiratory trees or inserted upon the cloaca, are wanting in all Cucumariae with 

 unequal tentacles ; but the readiness with which these organs are ejected by the 

 Holothurians, when they are alarmed or irritated, is such as to make it unsafe to 

 base a conclusion as to a specific difference upon their absence or presence. Semper, 

 on the other hand, Eeisen im Archipel der Philippinen, p. 47, assigns this smaller 

 size of the two medio-ventral tentacles as a generic property to the Cucumariae ; 

 but he also specifies the presence of this peculiarity in individual cases of particular 

 species as though it were not universally present. 



