$$ 91, 92. 
sive power, united with the action of the cloaca, enables them to receive 
into and expel from their interior the water of the sea. 
The internal branchiz of the Echiuridae consist of branchless tubes. In 
Echiurus vulgaris, the two branchiz, which are very movable and open 
into a kind of cloaca, have, on their exterior, infundibuliform, ciliated pro- 
tuberances; and to each of these there is internally a corresponding cili- 
ated sac, capable of being inverted. The very bright-red, vascular net- 
work which is spread over these branchiae, communicates with the great 
ventral vessel at the posterior extremity. 
ECHINODERMATA. 
92 TH.d 
§ 91. 
IL. Among the organs which are not exclusively respiratory, are the 
ambulacra of the Echinodermata pedata, and the oral tentacles of the Ho- 
lothurioidea and Sipunculidae, — organs which are used also for prehension 
and locomotion. ; 
These ambulacra and tentacles have always a cavity which communicates 
directly with the proper vascular, aquiferous system. Their whole interior 
is covered throughout with ciliated epithelium. ' 
This aquiferous system has, until recently, been taken by anatomists as 
a special vascular one, or confounded with it. Its water serves partly to 
distend the ambulacra and tentacles, as shown above ($ 77), and partly for 
respiration, which is performed by the vesicles over which ramify the 
branchial vessels. These vesicles are therefore like internal branchise, 
their vessels being bathed by the water of the sacs, and that of the cavity 
of the body. Usually this system consists of a ring situated between 
the vascular rays of the mouth, which sends canals to the oral tentacles 
and to the sides of the body. These canals always pass along by the rows 
of ambulacral vesicles, with which they communicate by lateral branches, 
§ 92. 
In the Echinodermata pedata, this aquiferous system has the following 
modifications : 
In the Crinoidea, and Ophiuridae,” only traces of it have been found. 
In the first, there is an apparently aquiferous canal for the tentacles, 
situated directly under their furrow. This may be regarded as forming a 
part of such a system. In Pentacrinus, it is simple, but in Comatuda, it is 
divided at several points by simple septa. ; 
In the Asteroidae, this system is highly developed, the central ring being 
provided with pediculated and often elongated vesicles. The main 
5 There is found, but inconstantly, it would 
appear, upon the trunk of the branchiew of some 
Holothurinae particular pedunculated coeca, which 
in Bohadschia marmorata have been regarded a3 
urinary organs by Jaeger (De Holothuriis, &., 
Yab. III. fig. 9, g.). Butthey require further 
investigation.* ‘ 
6 Forbes and Goodsir (Froriep’s neue Not. 
No. 392, p. 277, fig. 12, e. — 19). 
1 From the figures of Delle Chiaje (loc cit. Tav. 
*[§ 90, note 5.] For many new details upon 
the respiratory system of the Holothurioidea, see 
XXI. fig. 17) it wculd appear that Ophturus has 
an aquiferous system. 
2 Muller, Abhandl. d. Berl. Akad. 1841, p. 234. 
3 These pyriform vesicular appendages are al- 
ways situated between the principal vessels of the 
rays, varying both as to number and volume, and 
being sometimes entirely wanting. Astropecten 
bispinosus has only five; Asteriscus verrucu- 
latus, Astropecten pentacanthus, and Astera- 
canthion glacialis, have ten, in pairs. In this 
Miiller, Arch. 1860, p. 129-155 (Synapta, Chir 
odota, and Molpadia).— Ep. 
