66 Royal Society : — 



system, and arguments are brought forward to show that the orifices 

 usually supposed to discharge this office are in reality the exhalant 

 orifices of a water- vascular system. The positive arguments drawn 

 from the way in which fine injections thrown in by these orifices 

 distribute themselves throughout the visceral mass, and from the 

 relative position of orifices acknowledged to belong to a water-vascu- 

 lar system in other mollusks, are confirmed by a consideration of 

 the improbability attaching to the old tow, which regarded as ovi- 

 ducts in mollusca two canals, which lying one on either side of the 

 body, yet communicate freely with each other at no great distance 

 from their termination, and which lie far away from the lower seg- 

 ment of the intestinal tube. The inhalant aquiferous orifices are 

 considered to be indicated by a belt of parasitic animals impacted 

 in the foot tissue, as represented in one of the figures. 



2. In the second part of the communication, the structures are 

 indicated which the authors hold to be the true oviducts. One 

 large band which is seen at the spawning season as a prominent 

 ridge projecting into the calibre of the lower segment of the intes- 

 tinal tube, and two smaller ones, which are traceable from the com- 

 mencement of the intestine down to a point where its upper coils 

 are in close proximity to that part of its lower segment where the 

 former band ends in a club-shaped dilatation, are shown to dis- 

 charge this function. The method of dissection to be adopted for 

 the demonstration of these structures is given at some length, and 

 the following arguments are adduced in support of the view which 

 regards them as oviducts. A fine injection thrown into the largest 

 of the bands in question is seen to pass into the ovary, and is re- 

 cognizable under the microscope as contained within the limitary 

 membrane of its ultimate follicles. Its distribution, therefore, as 

 detectable at once by the naked eye and by the microscope, con- 

 trasts strongly with that of a similar injection thrown in by either of 

 the aquiferous orifices. Secondly : The condition of distension, 

 prominence, and intumescence of this band, coincides with similar 

 conditions in the ovary ; and from an acquaintance with the condi- 

 tion of the branchial marsupium's contents we are enabled always to 

 predict what will be found to be that of this band. Thirdly : At 

 periods when ova are being rapidly secreted by the ovary, ova are 

 to be found at all points within the whole length of these three 

 bands. The double oviduct at the oral and the single at the anal 

 extremity of the Lamellibranchiata, is what our knowledge of their 

 development would lead us to anticipate ; and the close connexion of 

 the principal oviduct with that latter outlet, and with the lower 

 segment of the intestinal tube, brings the anatomy of these bivalve 

 mollusks into exact correspondence with that of higher tribes in the 

 same series. 



What is said of the ovarian secretion and outlets, applies, mutatis 

 mutandis, to the testicular. 



