MR. F. D. DYSTER ON PHORONIS HIPPOCREPIA._ 253 



which for convenience may be called the artery. Along it the blood rushes upwards in a 

 powerful stream, until it arrives at the base of the lophophore, where it bifurcates, giving 

 a branch to each of the rami. These branches open into sinuses which extend all roixnd 

 the lophophore ; and a twig is given off to each tentacle. The blood pursues its course to 

 the extremity of the tentacles, which are provided with contractile vessels, tied down on 

 one side, free on the other. The progress of the blood is not uniform in the tentacles, as 

 it will be frequently seen to be ascending one Avhile it is descending another, and some- 

 times the stream may be observed to recede from one tentacle and then fill the adjoining 

 one instead of falling back into the general circulation. Two venous trunks open from 

 the sinuses above and behind the arterial branches, and then proceed downwards, half 

 encircling the oesophagus, till they unite in a large vessel on its neural surface. The 

 blood moves by pulsations in the artery, at the rate of from twelve to fifteen beats a minute, 

 the vessel contracting on it as it passes upwards, and remaining empty in the intervals 

 between the beats. The returning stream through the neural vessel is perfectly conti- 

 nuous. In the course of the body the neural and haemal vessels are connected by nume- 

 rous capillaiy loops ; and when the upper portion of the body is removed, the circulation is 

 quickly re-established through the loops nearest the point of scission, and carried on as 

 powerfully as before. 



The blood consists of a colourless liquor sanguinis, densely charged with red globules 

 of irregular shape and size, varying from cii'cular to elliptical, flattened and somewhat 

 concave on one side. In length they vary from s^-gVoth to -pTVotb of an inch. The thick- 

 ness is about 8 0^0 o th. All are provided with one, many with two nuclei of granular ap- 

 pearance, about 2oooo th of an inch in diameter. They are exceedingly flexible, and turn 

 about, double, elongate, and flatten when pressed for room by meetiug other gloliules in 

 the capillaries, exactly as globules of human blood do when seen coursing about under 

 thin glass. There are no colourless corpuscles ; and very careful watching detected no 

 Amoeba-]ike movements. They coagulate in masses which appear homogeneous, the nuclei 

 only remaining visible. Treated with acetic acid, the cell-lining contracts, and all the 

 globides assume a perfectly spherical form. There seems no ground for supposing that 

 any special heart-like organ is concerned in the circulation of Phoronis. At whatever portion 

 of the body section was made, after the shock of separation was recovered from, the pidsa- 

 tions of the haemal vessel were renewed with the same vigour as before ; and this occm-red 

 in the posterior extremity of one individual which was dug out to nearly its full extent. 



The ovary lies below the stomach, and is, I believe, single. It is a long cylindrical 

 vessel, pyi'iform at its base, perfectly transparent, and scarcely distinguishable except by 

 its contained eggs, which appear to be attached to the inner surface. The ova are slightly 

 elliptic, granular, about xog^th of an inch in diameter: the individuals of which the 

 ovaries were examined were all young ; and there was no difference in the size or deve- 

 lopment of the ova. No specimen was observed without an ovary ; but in only one 

 spermatozoa were found. The body of these measured from ygVotb to -nVotb of an inch, 

 with a filiform tail of equal length. 



The ova when deposited are white, spherical, about awtb of an inch in diameter, and 

 not tiliated. The oviduct lies above the rectum, on the haemal surface, immediately 



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