BIVALVES THEIR FECUNDITY. 349 



having seen, when examining some Kellia suborbicularis 

 in a saucer, several testaceous young ejected from the ano- 

 malous tube of one of the animals." Further observations 

 confirmed Mr. Clark in this opinion. * 



The bivalves, like the Mollusca in general, are capable of 

 reproduction at an early age and long before maturity. Of 

 the Cyclades the Rev. Leonard Jenyns says, " they have 

 the faculty of producing long before they are arrived at their 

 full growth, and even some individuals which are themselves 

 so immature as to possess hardly any of the distinguishing 

 characters of the species, frequently contain young of a 

 sufficient size to be seen from without through the trans- 

 parent valves." -J- Oysters spawn when they are only four 

 months of age, although they do not attain their full size 

 until after the lapse of three or four years. And the pro- 

 lificness of the class is prodigious. Leeuwenhoek reckoned 

 that there were ten million embryo young in an adult oyster, 

 Baster reduces the number to a hundred thousand, and the 

 reduction might be allowed without much weakening our 

 position, even had Poli not added his authority for its more 

 abundant fruitfulness. He says that an oyster may contain 

 one million two hundred thousand ova, and may give birth 

 to the contents of twelve thousand barrels ; so that the Rev. 

 William Kirby, with a naivete that might suit the author of 

 a prior century, concludes hence that " Providence has thus 

 taken care that the demands made upon them to gratify the 

 appetite of his creature man, shall not annihilate the race."J 

 " In the dissection of an Anodonta undulata nearly three 

 inches long," says Mr. Lea, " I met with the oviducts charged 

 with about six hundred thousand (as nearly as I could cal- 

 culate), young shells perfectly formed, both valves being dis- 

 tinctly visible with the microscope." Dr. Unger reckoned 

 in a full grown Unio pictorum three hundred thousand em- 

 bryos and young individuals ; and Sellius has made some 

 calculations which prove an almost incredible fecundity in 

 the Teredo. || These are sufficient and not exaggerated in- 

 stances of the prolification of the Conchifera, which would 



* Ann. and Mag. Nat. Hist. Ser. 2, iv. 143. Mr. Alder has, however, 

 questioned the uterine function of this siphon. Lib. cit. 245. 



t Monograph from Camb. trans, p. 10. See also Brown in Edinb. Journ. 

 Nat. and Geogr. Sc. i. 412, where he proves that Pisidiuin is viviparous. 



t Bridgew. Treat, i. 257. 



Edinb. New Phil. Journ. ix. 386. 



|'| De Tered. p. 15. The calculation made by Leeuwenhoek of the 

 number of young laid by the Common Mussel (Mytilus edulis) is to be 

 disregarded, for he mistook a parasitical zoophyte (Flustra dentata) for the 

 ova. Phil. Trans, abridg. v. 703 ; Select Works, i. 82. pi. 3. fig. 9. 



