ANATOMY OF PELECYPODA BI" HXK. -r.l 



tn have been dragged from tin.- slid! while tin- animal was alive) mav have had as oiie 

 of its results an alteration of tin- form i>t' thr kidney by the forward sin-inking of its 

 upper parts. AVhether this has Keen the case r not, the possibilit y that tin- form "I' 

 kidney presented may he unnaturally short in the longitudinal direction and di.Morted 

 by the forward and upward migration of its posterior end nniM nut lie lust .-ight of. 



The pericardium (Fig. 20, />.<:) is prolonged backwards along the limn- of the 

 kidney on either side uf the mid-line ; and. <m a level just in front of the niuntli ui' ihe 

 urinogenital canal, gives place at its extremity to the ivno-perieanlial funnel (Fig. L'u, 

 r.pc.d.). This passes upwards towards the remains of the addm-tor. parallel to the 

 pericardium, and shortly enters the proximal arm of the kidnev (Fig. _'<>. /-./-. 1. uhidi. 

 in turn, upon Hearing the adductor communicates with the distal arm. IJoth the ivno- 

 pericardial funnel and the proximal arm are complicated by pleating. The walls of 

 the distal arms are dosely folded and tabulated, presenting in section an almost solid 

 mass of renal tissue. In the area between the proximal arm and the pericardium thev 

 are in open communication with one another. The distal arm opens to the exterior 

 through a long tubular but dorso-ventrally flattened urinogenital canal (Figs. 21, ill'. 

 _':!.\, ]:, "!/.(-'.). The mouth of this canal lies under cover of the protuberant ventral 

 border of the kidney, at some little distance behind the termination of the attached part 

 of the gill-axis, vertically about half-way between the attachment of the reflected lamina 

 of the inner demibranch and the branchial nerve (Fig. 23A, B, l>r.n., /./.), and just above 

 the cerebro- visceral connective. The caual runs directly inwards beiieat h the kidney, and 

 is continued without interruption into the oviduct (Figs. 21, 22, 23, <>.(!.). In its roof, 

 vertically above the cerebro-visceral connective, is a large circular hole (the nephroproet) 

 (Figs. 21, 22, 23B, >:o.) giving access to the cavity of the distal arm of the kidney, and 

 in its floor opposite the anterior and mesial area of the nephroproet is the opening of 

 the male genital duct (Figs. 21, 22, 23A, m.d.). The urinogenital canal and both 

 genital ducts are strongly ciliated. 



The passage between the kidney and the uriuogeuital canal is apparently perfect I v 

 open and free, and offers little hindrance to the passage of the products of generation 

 into the kidney. In fact, in this particular specimen a bunch of ripe eggs was lodged 

 in the renal orifice, and others were scattered in various parts of the cavitv of the 

 kidney. 



It is not, however, reasonable to suppose that, under normal conditions, eggs are 

 discharged otherwise than down the uriuogeuital canal, though thev evidenllv can. 

 without difficulty, find their way into the kidnev in the case of any abnormal 

 convulsion of the body, such as probably took place when the animal was killed. 



The above arrangement of the renal and genital orifices is not that eommonlv met 

 with among the Anatinaeea. I'siialh all three dud open scparatelv upon the surface, 

 though often ijiiite dose together (4, p. 721. 10, p. 214, I6A. \>. 72). In P<tn</t>i;i 

 (8, p. 349) the renal din-t is separate, but the two genital duds open bv a common 

 orifice. 



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