1887.] 



ON CYCLESTHERIA HISLOPI. 



41 



against each other and their bodies revolved, so as to cross 

 and triturate the particles. At the same time the labrum is 

 lowered at short reprises and then thrown back against the 

 mandibles, thns continually conveying new particles within the 

 reach of the mandibles. The swallowing movements of the æso- 

 phagus when transferring prepared food to the intestine, are 

 very distinctly observed through the shell, whereas the in- 

 testine itself does not seem to perform any perceptible peristaltic 

 movements. 



D. Circulation. 



The blood is colourless, and contains nnmerous small roimded 

 blood-corpuscles, the course of which may be traced with compara- 

 tive ease, especially in young transparent specimens. By the con- 

 tractions of the heart, about 150 in a minute, the blood is expel- 

 led exclnsively from its anterior extremity, which, as stated 

 above, is prolonged to a short aorta, having at its base a val- 

 vular apparatus, which opens and closes -at regular intervals. 

 On leaving the open end of the aorta, the blood flows in two 

 different directions, one part anteriorly, the other posteriorhv The 

 considerable quantity of blood conducted to the anterior part of 

 the body is seen to flow down the sides of the head, partly 

 supplying its several appendages, partly running straight back 

 along its ventral side to* the region of the adductor muscle of 

 the shell. Here the blood enters the valves, being received 

 within the complicated system of canals occurring between their 

 two lamellæ. The other principal arterial current is seen runn- 

 ing from the heart backwards along the dorsal side of the 

 trunk, «immediately above the intestine; and, on reaching the 

 tail, it bends round and flows anteriorly along the ventral side> 

 sending ol£ it would appear. in each segment, lateral cur- 

 rents to the branchial legs. The blood thus conducted to the 

 several parts of the body and to the shell, returns to the heart 

 by two different ways. The considerable quantity of blood in- 

 troduced within the canal-system of the shell is at last received 



