Mr. W. Clark on the Pholadidje. 327 



not be understood ideally, as these animals have distinct visible 

 organs, the union of which, within themselves, produces the 

 male and female influences. I hesitate to concur in the state- 

 ment of some authors, that the sexes are distinct in the bivalves. 

 I think it is probable that this idea has arisen from the animals 

 being examined at different periods of the year. In the genial 

 months, the ovaria, and the virile membranous pouches, are dis- 

 tended and fully developed ; but in the winter season, when all 

 nature flags, and takes repose after the exhaustions of the sum- 

 mei*, and when even the influences of the " JEneadum Genetrix " 

 ai'e softened down, then the ovaria and the pyriform virile mem- 

 branes become obsolete : these two very different states may have 

 contributed to produce erroneous conclusions. We must, as I 

 have elsewhere observed, not forget the precept, 



" jEtheris et terras genitabile quserere temjius." 



I do not mention that I have quoted this line a second time, as 

 an apology for the repetition ; on the contrary, I mean to mark 

 the great importance in which it was held by the illustrious 

 author, who has in his work repeatedly used it or its equiva- 

 lent. 



The ovarium of P. dactylus is a conical organ, amalgamated 

 with the lower part of the body, having a pointed apex. Though 

 I applied the quicksilver, I did not satisfactorily make out the 

 oviducts ; they do not appear to be at the apex of the ovarium, 

 and I am inclined to think that they are situate at the junction 

 of the body with that organ. In many bivalves it is considered 

 that the ova, on issuing from their receptacles, are at once com- 

 mitted to the protection of nature. I almost think this idea is not 

 correct, and that the ova, after fecundation and exclusion from 

 the ovarium, are for some time committed to the protection of 

 the parent before final ejection. In some bivalves, as in Anodon 

 and the Mijtili, the ova are transferred to the interspaces of the 

 branchial laminse for maturation. In this species and its con- 

 geners we believe the ova pass from the ovarium into the crypts, 

 traceries and interweavings of the roof of the anal vault, and re- 

 main there separated from the ovarium, and undergo, mutatis 

 mutandis, precisely in the different seasons, the same phases and 

 aspects as I have mentioned concerning the ova in the ovaria of 

 the Dentalia, in my paper on that genus in the ' Annals,' the ani- 

 mals of which are strict hermaphrodites, as are the Chitons and 

 Patella ; and thus we see the propriety of placing those Gaste- 

 ropods as immediate sequences to the bivalves, in respect of na- 

 tural order. 



Teredo, Adanson. 



I submit for the consideration of malacologists a description of 



