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 1 . 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 2 , whilst in Daphnia 200 beats of the heart 

 in a minute were remarked by JURINE and STRAUS DURCKHEIM S . 

 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 

 VOGT 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 Cirri- 

 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 cirri; 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 Isopoda, 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 MILNE EDWAEDS Ann. des Sc. not. XL 1827, pp. -283 314 and pp. 

 352 393 ; MILNE EDWARDS Hist. nat. des Crust, i. pp. 94 105 ; LUND in OKEN'S 

 Ms 1829, s. 1299, A. D. KROHN (A stacus fluviatilis] ibid., 1834, s. 518 529, Taf. XIL 

 Beautiful figures of the heart and vessels in Astacus marinus, after the preparations of 

 HUNTER, are to be found in the Catalog, of tJie Physiolog. Series of comp. anat. in the 

 Museum of the Royal Coll. of Surgeons. Vol. n. 1834. PI. xv xvm. pp. 136 140. 



3 C. G. CARUS Von den dusseren Lebens'bedlngungen der weiss- und kaltbliitige* 

 Thiere. 1824, 4to. s. 83. The number of beats was increased by the stimulus of warmth, 

 but became fewer and irregular under the influence of galvanism. 



3 Mem,, du Museum v. pp. 412, 413. 



