210 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 gills (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. 152,7) lying in the ambulacral zones. The 
mouth is surrounded by a muscular ring, from which arise 
ten large, much-branched tentacles. The pharynx, or the 
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 6) 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 (c), rom which 
* In Hupyrgus and Kchinocucumis it is difficult to perceive any radia- 
tion in the body except in the unbroken 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 water-vascular system of Echinoderms, 
