and Oviducal System in the Lamellibranchiate Mollusks. 451 



2ndly. The external orifice of the organ of Bojanus may be 

 seen in a living Anodon (and, from its lying exposed in the gill- 

 cavity, with yet greater ease in a Unio margaritifera) to execute 

 movements of alternate opening and shutting, similar in charac- 

 ter to those executed, as has been repeatedly noticed, by the 

 analogous organ in the Pteropoda. These movements are re- 

 peated as frequently as once in every ten seconds (or oftener) in 

 the Unio margaritifera) and they possess, there can be little 

 doubt, in these as in other mollusks, the power of filling with 

 water the cavities into which it leads. 



3rdly. The glandular portion of the compound organ of 

 Bojanus has its opening into the pericardium guarded by a 

 funnel-shaped projection which acts as a valve looking heart- 

 wards, and offers resistance consequently to fluid passing out- 

 wards from that lacuna. 



4thly (Experiment 3). Fluid thrown in by the external orifice 

 of the organ of Bojanus, as it is either artificially, as in the 

 Anodon, or naturally, as in the Unio margaritifera, exposed in 

 the gill-cavity, finds its way even more easily into the pericar- 

 dium than fluid thrown, as already described, into the pericar- 

 dium finds its way into the gill-cavity by the reverse route. 

 This experiment is but an imitation of what we may suppose to 

 take place whensoever the animal by opening its valves dilates 

 its pericardial space. As an immediate consequence of this dila- 

 tation, water is ingested into the blood-vascular system, and is 

 forthwith applied to the purpose of distending the foot and pro- 

 truding it through the opening valves. 



Up to this point our views are in accordance with those 

 adopted by several authors, though we are not aware that our 

 method of proof has been employed by any other observers, so 

 far as its detailed application is concerned. 



We will now proceed to give our reasons for supposing that 

 another system of tubes comes in aid of the blood-vascular 

 system, and receives from it the fluid which that system has 

 been the means of taking up in the manner described. Our 

 arguments will go to show that water is transferred from the 

 blood-vessels in the foot of the freshwater mussel to another set 

 of vessels, the main stem of which has the additional function of 

 outlet to the generative gland. As, however, Von Hessling* 

 holds that the system of pores in the foot plays no inconsider- 

 able part in the work of supplying the distending foot with 

 water, acting in aid of, and in alliance with, the system of the 

 organ of Bojanus, and, with Agassiz and Von Rengarten, as 

 already cited, holds this office to be exclusively discharged by 

 this system of pores and inlets, we will begin by stating our 

 * Perlmuscheln und ihre Perlen, p. 238 et seq. 



30* 



