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XLVI. Memoir on fome Peculiarities in the Anatomy and 

 Phjifiology of the Shark, fartimlarly rej'pccling the Pro- 

 dudtion "of its Young, Bj Dr. Mitchill, of New York*, 



XxLTHOUGH the generation and multiplication of ani- 

 mals have fo long exercifed the attention of philofophers, the 

 whole fubje£t remains involved in intricacy and indillinftnefs. 

 The maxim laid down by Harvey, and adopted by Linn^us, 

 of 077ine animal ex ovo, that every animal proceeds from ail 

 effg, has, perhaps, been too generally received, fince nume- 

 rous fads, related by Mr. Bonnet, in his work entitled Con- 

 JidiTaiions fur les Corps Organifis, e\ince the propagation of 

 animals, in a great variety of cafes, from germs. Notwiih- 

 ftanding the multiplicative powers of animals have been thus 

 traced to ecgs and germs, yet a popular dillinction ftill pre- 

 vails to a tH)nfidcrable extent, of clafling animals that propa- 

 gate their fpecies by means of genital organs, into oviparous 

 and viviparous. 



The great difcovery of Haller, that the membrane covering 

 the yolk of an egg was really a continuation of the membrane 

 covering the inteltines of the chick, had not only given coun- 

 tenance to the idea of the pre-exi(tencc of the embryo, but 

 has fliown that animals, whether of the oviparous or vivi- 

 parous kinds, really propagated their fpecies in pretty much 

 the fame way. 



Amidft the different modes in which the embryo and its 

 membranes are organized in difiercnt animals, there leems 

 to be one cafe which has not been hitherto defcribed with 

 the accuracy and niinutenefs which its fmgularity defervt?s : 

 the genus of the fqnalus, which includes all the animals of 

 the (liark tribe, has fome peculiarities which make fhefe ani- 

 mals approach both to the oviparous and viviparous claffes, 

 without, however, belonging ftridly to either. 



It had been known a long time, that the young of the 

 fhark had fomething in their (irnfture confiderai)ly different 

 from any other creatures, and figures of them have been given 

 by Edwards in his Natural Hiiiory, and probably coj^ied from 

 thence into the Encyclopaedia; but there has noi been, as yet, 

 any dilfec^tion of ihefe animals in this period of their exig- 

 ence, nor any explanation of their phyfiology that I know of. 

 It is the obic6t of this flioft memoir to explain the ftruc^ure 

 and fimdions of the fcetiis of a fpecies of {liark found fre- 

 quently along the coaft of New-York, in the waters of the 

 Atlantic, during the fummer months. About two years 

 * Communicated by the Author. 



ago? 



