ENTOMOSTRACA OF MINNESOTA. 159 



favoring the impression that there is here a veritable opening. The 

 outflowing blood stream is bounded at first by the membrane above 

 mentioned, which is farther on reflexed onto the shell and intestine so 

 that the streams in the head flowing just under the shell are separated 

 from the deep dorsal stream flowing from the heart.* This main cur- 

 rent passes to the region of the eye between the horns of the ccBca of 

 the alimentary canal, and thence beneath the stomach, and here 

 divides, part becoming external and a deeper part passing under the 

 intestine, thence in front of the heart, flows into the deep sinus which, 

 as before said, passes beneath this organ. Other portions of the 

 returning stVeam flow around the angle of the union of the head and 

 body and constitute a stream just above the feet in which the current 

 flows vigorously. 



Yet other portions flow into the region of the shell gland and are 

 united with blood which here passes through the numerous sinuses 

 described by Claus ('75) as surrounding this organ, and thence flows 

 into the abdomen, uniting with the other two streams. A part also 

 of the current in the head flows into the antennse where it follows a 

 deep course through the basal joint in which the corpuscles may be 

 seen to emerge to the surface from two points where are spaces be- 

 tween the powerful muscles, the first being near the base and the sec- 

 ond near the extremity of this joint, and then to return and join the 

 superficial current. 



The corpuscles appear to enter the rami very rarely if at all. That 

 part of the superficial stream which reaches the interior of the peri- 

 cardial chamber passes between the muscles of antennae and jaws, and 

 seems to find its way into the great current beneath the heart, though 

 I have also thought to have seen it flow directly into the pericardial 

 space as the lateral superficial streams do. That part of the super- 

 ficial stream which reaches the posterior margin of the shell returns 

 through a canal formed by the walls of the shell and the brood space, 

 between the " stutzbalken " of which the blood corpuscles can be seen 

 to glide more rapidly than in the free lateral spaces. 



Lastly, it only remains to follow the fortune of the strong stream 

 flowing along the neutral surface of the abdomen. The strong current 

 flowing beneath the heart enters a broad sinus which lies over the in- 

 testine and extends for over a third of its length, where its walls unite 

 with the surface of the intestine above and thus open downward on 

 cither side. 



The stream thus directed flows toward the openings of the base of 

 the feet. The structure of the branchire has not yet been clearly de- 



* In Pas ithearecli7-ostris this sepiuva is easily seen as a swaying membrane, which near the eye is 

 leflexed to the top of the shell. 



