970 PROF. OWEN ON THE [NOV. 19, 



For the different views which have been propounded as to the 

 nature and function of this complex siphon, reference may be made 

 to the authors cited, p. 966. Some of these views were based on the 

 partial knowledge of its structure at the date of the first dissection 

 of the Pearly Nautilus. 



The true structure of the siphon in Nautilus pompilius is rarely 

 preserved ; the somewhat loose calcareous matter by which the 

 membranous part is iucrusted is commonly lost with that part in the 

 dry cast-off shells. The calcareous incrustation is apt to be dis- 

 solved, like that of the mandibles in Valenciennes' s specimen, by the 

 acetous change of the alcohol when charged with soluble parts of the 

 animal during a prolonged transit to a European museum. 



Fig. 3. 



Nautilus striatus. 

 Section of part of shell. 



When cataloguing, in 1854 and 1855, the Hunterian Cephalopods, 

 I saw sufficient to supplement the description of the siphon in the 

 • Memoir on the Nautilus,' as follows : — " An artery and vein are 

 assigned for its life and nutrition, and to extend a low degree of the 

 same influences to the shell ; but the structure of the membranous 

 siphuncle presents, beyond the first chamber, an inextensible and 

 almost friable texture, apparently unsusceptible of dilatation and 

 contraction ; it is also coated beyond the extremity of the short 

 testaceous siphuncle with a thin calcareous deposit" 1 . The fact of 

 this incrustation has been ascertained, independently, by Prof. 

 Vrolik. The subject of his memoir in the volume cited iu note I, was 



1 Descriptive Catalogue of the Fossil Organic Eemains of the Invertebrata 

 contained in the Museum of the Royal College of Surgeons of England, 4to, 

 1856, p. 29. This volume was not issued until all the invertebrate fossils were 

 described ; and the first sheets were printed off before the ' M^moires de la 

 Society Linneenne de Normandie,' vol. x. 1855, came to my hands. 



