192 PHOLADIDjE. 



season, when all nature flags, and takes repose after the 

 exhaustions of the summer, and when even the influences of 

 the "^Eneadum Genetrix" are softened down, then the 

 ovaria and the pyriform virile membranes become obsolete : 

 these two very different states may have contributed to pro- 

 duce erroneous conclusions. We must, as I have elsewhere 

 observed, not forget the precept, 



" .ZEtheris et terrse geuitabile quserere tempus." 



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 illus- 

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

 equivalent. 



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 committed to the protection of 

 nature. This idea is mainly correct, but in certain species, 

 for example in the Kelliada, &c., the ova, after fecundation 

 and exclusion from the ovarium, are for some time committed 

 to the protection of the parent before final ejection; in 

 Anodon and the Mytili, they are transferred to the branchial 

 laminae for maturation. In the Pholades, we believe the ova 

 pass at once from the ovarium into their native element. 



Since the above observations were written, Messrs. Alder 

 and Hancock have dissented from my theory ; I replied by 

 the following letter : 



To the Editors of the Annals of Natural History. 

 GENTLEMEN, Exmouth, September 1853. 



I request permission to reply to Messrs. Alder and Han- 

 cock's comments in the ' Annals of Natural History/ vol. viii. 



