$$ 193, 194. THE ACEPHALA. 209 
lacunae situated at the base of the branchiae, and into which it thence 
passes, 
CHAPTER VII. 
RESPIRATORY SYSTEM, 
§ 193. 
With all the Acephala, the blood, just before returning to the heart, 
passes through a branchial, or distinctly respiratory organ, which, either 
simple or multiple in structure, is always hidden in the cavity of the man- 
tle. The renewal of water takes place by special openings of the body, or 
through the slits of the mantle, which are often prolonged into two respir- 
atory tubes. One of these openings is for the ingress, and the other for 
the egress of the water, and their currents carry in and out, respectively, 
food and faeces. In the cavity of the mantle, the water circulates in a 
definite direction and passes over the branchiae by means of the cilia cover- 
ing their external surface. 
§ 194. 
The Branchiae of the Acephala are formed after four different types: — 
1. With Salpa, there is one only of these organs which stretches, from 
above downwards and from before backwards, across the cavity of the body. 
The water enters through an anterior orifice which is usually valvular, and is 
expelled through a posterior opening by the contractions of the body.” 
The branchia itself, which, near the heart, is bent a little in front at its 
lower posterior extremity, consists of a narrow band having upon one of 
its sides numerous transverse, thickly-set folds.”. Its remaining portion is- 
flat, or the lateral borders are rolled up like tubes.” The branchial ves-. 
sels are ramified in the interior, communicating, at the superior extremity 
and has figured it very beautifully ; see his Des- 
criz. &c. Tav. LXXV. tig. 6, and Tab. XC. fig. 1, 
2 (Mantle of Pecten and Solen), Wav. LXXXIX? 
fig. 11 (foot of a Mactra). — 
The vascular net-work which Po/i (loc. cit. Tab. 
XXXVIII.) has figured in the mantle of a Pinna, 
is probably only one of aquiferous canals. 
I shall again (§ 195) allude to this confusion 
between the blood and aquiferous vessels.* 
1 These respiratcry motions aid also for the lo- 
somotion of Salpa ; for, when water escapes by the 
* [§ 192, note 11.) This lacunal system is well- 
marked with Teredo according to Quatrefages, 
who denies that these animals have a proper venous 
- system. The grounds of this conclusion are, that 
these lacunae are always filled by injecting the 
18* 
posterior orifice, the animal closes the valve of the- 
anterior one, so that the body is thrown forwards. 
On this account the cavity of the body is often 
called natatory. 
2 See Cuvier, and Savigny, loc. cit. 
3 Salpa coxtata, and maxima. 
4 Salpa pinnata, cylindrica, octofora. When 
the branchia is contained in a tube it has often been 
Sompared. to a Trachea ; see Savigny, loc. cit. Pl. 
v 
heart, and on the other hand, all the other lacunae 
and the arterial system beside may be filled by in- 
jecting through one lacuna; see Mémoire, loc. cit. 
p. 55. — Ep. 
