$$ 89, 90. THE ECHINODERMATA. 91 
CHAPTER VII. 
RESPIRATORY SYSTEM. 
§ 89. 
The respiratior of the Hchinoderms is performed in various ways. These 
are: 1, By exclusively respiratory branchiae. 2. By organs serving 
at the same time other functions. 3. By means of water passing 
through the openings of the skin into the cavity of the body, and aérating 
the blood through the capillary vessels of the viscera. 
With the Asteroidea, Synaptinae, Sipunculidae and Nchiuridae, every 
individual has always two of these modes of respiration, and sometimes 
all three, as with the Echinidae and Holothurinae. 
§ 90. 
I. Organs which are exclusively respiratory are found in the Hchi- 
nidae, Holothurinae, and Hchiuridae. They consist of external branchiae 
in the first, and internal in the last two. 
The external branchiae of the Echinidae are situated upon the soft 
membrane of the mouth, being formed of five pairs of arborescent, hollow 
lobules.” They are contractile, but cannot be retracted within the body. 
They are covered both internally and externally with ciliated epithelium. 
The cavity of each communicates with that of the body by a large ori- 
fice situated on the internal surface of the oral membrane.” By this 
means they are bathed with water upon both of their surfaces. Their 
walls contain a coarsely reticulated calcareous skeleton,® and without 
doubt, also a capillary net-work belonging to the branchial vessels. 
The internal branchiae of the Holothurinae arise as two tubes from the 
cloaca of the intestinal canal, and send off, through the whole cavity of 
the body, numerous coecal branches. In Holothuria tubulosa, one of 
these tubes is closely connected with the turns of the intestine, while the 
other is attached to the inner walls of the body. With the first, espe- 
cially, may be perceived the ramifications of the branchial vessels. They 
are also covered with ciliated epithelium, and their contractile and expan- 
1 The ramified organs of the Echinidae, already 
known by Tiedemann (loc. cit. p 78, Taf. X. fig. 
5, d.d.) and Delle Chiaje (loc. cit. IL. p. 338), 
have been more exactly described by Valentin 
(Monogr. &c. p. 82, Pl. IV. fig. 57; Pl. VIII. fig. 
42), and by Erdl (Wiegmann’s Arch. 1842, I. 
p. 59, Taf. If. fig. 12, 13). 
2 Valentin, loc. cit. Pl. VII. fig. 135, 1. . 
8 Valentin, loc. cit. fig. 143 ; and Erdi, loc. cit. 
fig. 13.* 
4The branchiae of Holothuria tubulosa have 
*[§ 90, note 8.] See, in this connection, Miller 
(Arch. 1850, p. 122), who has confirmed Vu‘en- 
been very well described by Tiedemann (oe. cit.. 
p. 11, Taf. Il. or Wagner Icon. zoot. Tab. 
XXXII. fig. 9), and by Delle Chiaje (loc. cit.. 
Tav. VIII. [X.). See also Atlas Zool. du Voyage: 
de PAstrolabe. Zoophytes, Pl. VII. fig. 2, 9, p-. 
(Holothuria ananas) and Pl. VII. fig. 38, e (Clad+ 
olabes spinosus). Pentacta doliolum has simi- 
lar organs. According to Cuvier (Anat. Comp. 
VII. 1840, p. 536) there is only a single branchia. 
in the other remaining Holothurinae. 
tin’s observations as to the structure of the exterx 
nal gills. — Ep. 
