HOLOTHUROIDEA. 263 



tidae and Molpadiidae, which are without tube-feet, are 

 burrowers. 



The skin in some forms secretes a slimy substance, which in 

 some cases appears to be used for entangling small food organ- 

 isms. In Pseudostichopus mollis and occultatus the body is 

 covered with the shells of Foraminifera. 



They feed on the smaller marine animals, which in the 

 Dendrochirotae are collected and carried to the mouth by the 

 large tentacles. These tentacles are used for this purpose one 

 at a time. The two small tentacles are applied alternately over 

 the mouth so as to close it or wipe it in the intervals between 

 the introduction of food by the large tentacles. The Aspido- 

 chirotae fill their intestine with sand, which they eject from the 

 anus together with the current of water from the respiratory 

 trees. It is worthy of notice that many Holothurians (especially 

 the Aspidochirotae) have the power when irritated of ejecting 

 through the anal opening the alimentary canal (and its appen- 

 dages) which breaks off behind the vascular ring and in the 

 region of the cloaca. They are able to regenerate the parts so 

 lost, sometimes with considerable rapidity. In some cases this 

 ejection includes the gonad, the calcareous ring and tentacles. 

 The ejected organs seem to be distasteful to other animals, and 

 if taken up are soon rejected. This ejection of the viscera is 

 said not to occur in Cucumaria or in the Elasipodidae. In the 

 Synaptidae the body, when irritated, breaks into several pieces 

 by violent muscular contractions of the body wall. The an- 

 terior of the pieces so produced is able to regenerate the rest of 

 the body. Asexual reproduction by division is said to take 

 place in Cucumaria planci, etc.* 



Of parasites found in Holothurians may be mentioned Ento- 

 valva mirabilis, a bivalve mollusc living in the pharynx of 

 species of Synapta (vol. i. p. 349), the Gastropods, Eulirna and 

 Stylifer in the gut and on the skin of various Aspidochirotae, 

 Entoconcha in the body cavity (Synapta and Holothuria), and 

 Entocolax from the inner side of the body wall of Myriotrochus 

 rinkii (vol. i. p. 403). Finally the remarkable commensal 

 Ficras/er, a Teleostean fish, lives in the right respiratory tree 

 of Aspidochirotae (vol. 2, p. 227). 



They vary in length from 5 to 60 cm. (Cucumaria frondosa 



* Chadwick, Proc. and Trans. Liverpool Biol. Soc., 5, 1891, p. 81. 



