42 



G. 0. SARS. 



[No. 1. 



by two longitudinal sinuses passing along its dorsal side, the 

 anterior rather short, the posterior occupying the greater part 

 of the dorsal line. In the anterior sinus, the blood flows back- 

 ward, in the posterior forward, the two currents meeting at 

 the place where the body is connected with the shell dorsally. 

 Here both currents suddenly bend down, the one on the an- 

 terior, the other on the posterior side, and pour out the blood 

 into the pericardial sinus, whence it passes into the heart 

 through the lateral valvular openings. The remaining part of the 

 blood, introduced into the trunk and the tail, is at last received 

 within a roomy sinus, occupying the upper part of the dorsal 

 side of the trunk and limited from the arteria! dorsal sinus by 

 a longitudinal ligament extending from the lower side of the 

 heart to the tail. This blood-sinus is apparently fed in each 

 segment of the trunk by a pair of ascending currents from 

 the branchial legs. The blood contained in the above-men- 

 tioned sinus flows from behind forward, or opposite to that 

 contained in the arterial sinus, and for the most part is in- 

 troduced into the heart through its posterior extremity. though 

 some would also seem to enter the posterior pair of the lateral 

 valvular openings. 



The course of the blood within the several limbs is nott 

 easy to examine in the present form, concealed as they are fo» 

 the greater part by the shell. In the antennæ, however, wkich 

 at times are more or less completely exserted beyond the shell, 

 the blood can be distinctly seen passing along the upper edge 

 of each branch to the extremity, then turning round, and flow- 

 ing back along the lower edge to the scape. 



E. Respiration. 



It has been generally admitted that the respiratory function 

 in all the Branchiopoda is performed by the legs, which for this 

 reason have been termed branchial feet. Of the several parts 

 composing the legs, the sac-like basal appendage is undoubtedly 

 the only one morphologically answering to the gills in higher 



