606 CLASS X. 
These convey it into sinuses situated in the middle of the body 
or along the feet, and from which it flows to the gills. From the 
gills it returns to a sinus that surrounds the heart, and often in the 
ten-footed crustaceans is described as a pericardium. On the dorsal 
surface of the heart are fissures, which during the diastole of the 
organ afford an entrance to the arterial blood with which this sinus is 
distended}. The blood of crustaceans is whitish or purple, sometimes 
red, as in Apus. The velocity of the circulation is very different 
in different families of this class. CArus, in the cray-fish, observed 
51 beats in a minute?, whilst in Daphnia 200 beats of the heart 
in a minute were remarked by JuRINE and Straus DurcKHermM?. 
The respiratory organs in the crustaceans consist of gills, which 
‘however are not met with in all, so that in some the skin itself 
appears to be the only organ of respiration. Also it is probable 
in a few that, at the same time that distinct gills are present, the 
skin is still partly serviceable for respiration, as in the lateral parts 
of the shield-like shell, in which the blood forms numerous currents, 
in Apus (according to ZADDACH) and in Argulus, in which last genus 
Voat regards these parts as the sole seat of the respiratory func- 
tion. The gills have the form either of plates that, consisting of two 
membranes, are properly flat sacs, or of filaments. In the Cirrd- 
pedia both forms are met with; in Anatifa (and the other pediculated 
genera, Lepadicea) there are two or more pairs of soft conical fila- 
ments which, with the point turned upwards, are situated at the 
base of the pedicle of the cérr7; whilst in the non-pediculated genera, 
the sea-acorns (Balanidea), fringed plates at the inside of the mantle 
are present. In many other genera, especially in the Lsopoda, the 
gills appear under the simple form of certain pairs of flattened sacs ; 
at the abdomen the feet are composed of two plates, of which the 
1 Compare on the circulation of the crustaceans amongst others the observations 
of AuDoUIN and Minne Epwarps Ann. des Se. nat. x1. 1827, pp. 283—314 and pp. 
352—393; Minne Epwarps Hist. nat. des Crust. 1. pp. 94—105 ; LUND in OKEN’S 
Tsis 1829, s. 1299, A. D. KRroun (Astacus fluviatilis) ibid., 1834, s. 518—529, Taf. x11. 
Beautiful figures of the heart and vessels in Astacus marinus, after the preparations of 
Hunter, are to be found in the Catalog. of the Physiolog. Series of comp. anat. in the 
Museum of the Royal Coll. of Surgeons. Vol. 11. 1834. Pl. XV—xviiI. pp. 136—r40. 
2C. G. Carus Von den dusseren Lebensbedingungen der weiss- und kaltbliitigen 
Thiere. 1824, 4to. 8.83. The number of beats was increased by the stimulus of warmth, 
but became fewer and irregular under the influence of galvanism. 
3 Mém,. du Muséum Vv. pp. 412, 413. 
<i 
