STATE GEOLOGIST. 31 



druse der Daphuien) and thence flows into the abdomen, uniting 

 with the other two streams. A part also of the current in the head 

 flows into the antenua3 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 between the powerful 

 muscles, the first being near the base and the second near the ex- 

 tremity 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 pericardial chamber passes between the muscles of antennas 

 and jaws and seems to find its way into the greac current beneath 

 the heart, though I have also thought to have seen it fiow directly 

 into the pericardia] space as the lateral superficial streams do. 

 That part of the superficial 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 Avhich lies 

 over the intestine 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 either side. 



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

 the feet. The structure of the branchiae has oot yet been clearly 

 •described. Instead of nearly spherical or oval chambers they 

 are really tubes which connect, on one hand with the opening 

 above, and below with the general cavity of the limb, whence the 

 blood returns to the abdomen. The current is very rapid through 

 these tubes. The blood having been returned to the ab- 

 domen, courses in the well known manner through the post-ab- 

 domen and flows over the intestine, thence over the back-flowing 

 stream to the posterior lower opening of the pericardial chamber. 



The study of the actions of the heart is rendered more difficult 

 by the fact that in order to secure the greatest possible transpar- 

 ency, the living animal must be covered and a little pressure ap- 

 plied, which is frequently attended with abnormal variations of the 

 •circulation. In particular if the usual exit of the blood be stopped 

 by the c«ca of the intestine, as is frequently the case, the opera- 

 tion of the heart may be reversed, when a vigorous stream may be 



