Mr. Gray on the Animal of ArgonaUta. 38.5 



Mr. Gray exhibited young shells of Argonauta Argo and Arg. hi- 

 ans, with the view of calling the attention of the Society to a new 

 argument in favour of the opinion that the animal (Ocythoe) found 

 in the shells of this genus is parasitic. This argument is founded on 

 the size of what Mr. Gray has termed the nucleus of the shell, viz, 

 that original portion of it which covered the animal within the 

 egg, and which is usually found to differ in surface and appearance 

 from the remainder of the shell formed after its exclusion from the 

 egg. In the specimens exhibited Mr. Gray described the nucleus as 

 blunt, rounded, thin, slightly and irregularly concentrically wrinkled, 

 and destitute of the radiating waves which are common to the adult 

 shells of all the species of this genus. These waves he stated to 

 commence immediately below the thin hemispherical tips, and he 

 therefore entertained no doubt that those tips constituted the nucleus 

 of the shell, and covered the embryo of the animal at the period of 

 its exclusion from the egg. Judging from the size of this portion of 

 the shell, which in one of the specimens measured nearly one third 

 of an inch in diameter, and was consequently many times larger than, 

 the largest eggs of the Ocythoe found within the Argonaut shells, 

 Mr. Gray inferred that it must have been produced by an animal 

 whose eggs are of much greater magnitude. The Ocythoe cannot 

 therefore, he conceived, be the constructor of the shell, and its true 

 artificer still remains to be discovered. Mr. Gray further remarked, 

 with reference to Poll's statement that he had observed the rudiment 

 of a shell on the back of the embryo of Ocythoe examined by him, 

 that he has himself uniformly found, in all the eggs of Mollusca which 

 he has examined, the shell well developed, even befoife the develop- 

 ment of the various organs of the embryo. With respect to the ar- 

 gument derived from the want of muscular attachment, he observed 

 that the animal of Carinaria (to which he considered it probable that 

 that of Argonauta is most nearly related), although firmly attached 

 to the shell while living, separates from it with the greatest ease 

 when preserved in spirits, being from its gelatinous nature very rea- 

 dily dissolved. These circumstances, he conceived, might fairly ac- 

 count for the animal of Carinaria having been, until very recently, 

 unknowa, and for that of Argonauta still remaining undiscovered. 



November 11, 1834. — A specimen was exhibited of a species of 

 Monacanthus, Cuv., remarkable for having on each side of the body, 

 about midway between the pectoral and caudal fins, a bundle of long 

 and strong spines directed backwards. The species was figured in 

 Willughby's * Historia Piscium,' and a description of it by Lister is 

 contained in the Appendix to that work ; but it appears not to have 

 been noticed by subsequent observers, and to have been altogether 

 overlooked or rejected by systematic writers. Lister's specimen of 

 the Fish was preserved in the collection of William Courten, the 

 founder of the museum which became subsequently the property of 

 Sir Hans Sloane, and eventually formed the basis of the British Mu- 

 seum : that brought under the notice of the Meeting belongs to the 

 Museum of the Army Medical Department at Chatham, and was 

 exhibited with the permission of Sir James Macgrigor. It was ac- 



Third Series, Vol. 6. No. 35. May 1835, 3 D 



