226 Royal Society . 



Cardium edule, Tellina solidula, Mactra stultorum, and Donax ana- 

 tina, I have precisely verified my previous conclusions. 



On throwing injections into the genital orifices, the sexual glands 

 have become turgid ; and on examining fragments of such injected 

 genital glands microscopically, the injected substance was seen mixed 

 with the ova or spermatozoa. These facts may be observed with 

 especial ease in Cardium edule. 



In addition to this, I have seen ova actually laid by living females 

 of Modiolce and My till, one of the valves of whose shell was removed, 

 on irritation of the genital orifice ; and in others the ova or the 

 spermatic fluid may be made to pass out of their orifices, at the 

 breeding season, by pressing gently upon the foot. 



In Spondylus yaderopus the genital orifice is situated in the sac 

 of Bojanus, and I had great difficulty in finding it when investigating 

 this subject. It was, in fact, only by chance that I opened the sac 

 of Bojanus and observed a little rose-coloured cylinder issuing from 

 an orifice in its interior. This cylinder, like a thread of vermicelli 

 in aspect, was composed of reddish ova mixed with mucus, and 

 agglomerated. I might multiply examples ; but it seems to be use- 

 less to do so, for I should simply reproduce the facts which I have 

 brought forward in the memoir which I published in the * Annales 

 cles Sciences Naturelles/ on my return from a long stay in the 

 Balearic isles. 



In this memoir, besides, I have not merely drawn attention to the 

 circumstance that after oviposition the aspect of the gland changes 

 completely, which might lead an observer to mistake the apparatus 

 of reproduction for something quite different, but I have given 

 figures of this condition of Pecten varius, &c. In fine, I believe that 

 the structure of the male and female organs of the Lamellibranchiate 

 Mollusca is such as it was described to be before the observations of 

 Messrs. Rolleston and Robertson. 



But does the system of aquiferous vessels, whose occurrence in the 

 Mollusca has been sometimes admitted, sometimes denied, really 

 exist in the Acephala? In the abstract to which I refer, those cita- 

 tions, which doubtless existed in the memoir, have not, and probably 

 could not have appeared. It is well known that the belief in this sup- 

 posed aquiferous system has been gradually becoming weaker. The 

 necessity of explaining the extreme dilatation and contraction of the 

 bodies of molluscous animals led anatomists to seek for and describe 

 such a system ; but at present the explanation of these facts is found 

 in the direct mixture of water with the blood, or the ejection of the 

 latter liquid. MM. Leuckart and Gegenbaur have made observations 

 tending to prove the occurrence of this process in the Pteropods ; M. 

 Langer of Vienna has published a special memoir on the circulation 

 of Anodon, and the great point he makes out is the passage of water 

 into the blood by the intermediation of the organ of Bojanus. I 

 believe that I have demonstrated in Dentalium the orifices by which 

 the direct communication of the circulatory apparatus with the ex- 

 terior of the body takes place ; and lastly, 1 have found a Gasteropod, 



