1-38 ZOOLOGY. 



treme low-water mark to a depth of fifty fathoms. It is of 

 a tan-brown color, from six inches to nearly a foot in^ 

 length, and in its form and the corrugations of its tough, 

 leathery skin resembles a cucumber in nearly all respects 

 except "color. There are five series of ambulacral feet, each 

 series consisting of two irregular rows. Around the mouth 

 is a circle of ten much-branched tentacles or gUls (homolo- 

 gous with the ambulacral feet). 



On laying the body open by making a cut extending from 

 the mouth to the vent, the thick muscular walls of the body 

 may be observed, and the general relations of the viscera to 

 the body-walls, which have nothing of the radiate arrange- 

 ment of parts, so clearly marked in the other Echinoderms,- 

 the ambulacra, tentacles, and longitudinal muscles alone be- 

 ing arranged in a radiate manner.* Unlike other Echino- 

 derms, the madreporic body is internal, and there is a ca- 

 pacious cloaca or rectum, and a large vent. 



On the inside of the body-walls are numerous small cir- 

 cular (transverse) muscles forming slight ridges, which serve 

 to contract the body, and five double large longitudinal 

 muscles (Fig. 89, T) lying in the ambulacral zones. Th& 

 mouth is surrounded by a muscular ring, from which arise 

 ten large, much-branched tentacles. The pharynx, or thfr 

 portion corresponding to " Aristotle's lantern," of the sea- 

 urchin is broad and short, with five large retractor muscles- 

 (r) originating from the ambulacral or longitudinal muscles 

 on the anterior third of the body. The stomach is short, 

 not much wider than the intestines, with well-marked trans- 

 verse folds within. The intestine ( i) is several times longer 

 than the body, with longitudinal small folds, and held in 

 place by a large, broad mesentery which accompanies the in- 

 testine through the greater part of its length. The intes- 

 tine terminates suddenly, in a large cloaca (t), from which, 



* In Eupyrgus and Ekliinoaicumis it is difficult to perceive any radia- 

 tion in the body except in the unbrolven circle of tentacles, while in 

 Sipunculus and allied worms (Gephyrea) the tentacles form a complete 

 circle, and these worms have a ring-canal and an imperfect or rudi- 

 mentary system of vessels thought by some authors to correspond to 

 the watervaSLular system of Echinoderms. 



