19 



near which they were inserted, and lost in the mantle. Here, therefore, a strong 

 analogical argument is afforded to those who object to the theory of the Argonaut 

 shell being secreted by, or forming an integrant part of the Cephalopod which 

 inhabits and deposits its ova in it ; for it is difficult to suppose, after \dewing 

 the uniform manner in which the shell is attached to the body in other Cepha- 

 lopods, and the regular relation subsisting between the means of attachment and 

 the part to be attached, that in this instance, where the shell is external, hke 

 that of Nautilus, and developed in a degree second only to it. Nature should, if 

 it were really developed by the Ocythoe, have reduced the ordinary means of at- 

 tachment to a lower degree even than in Octopus. 



In Nautilus Pompilius the crm-a or pillars of the funnel {m. pi. 1 ; h. pi. .5.) are 

 more distinctly separated from the muscles of the shell than in any of the pre- 

 ceding genera. They commence from the membrane that connects the mantle 

 with the back of the hood, inchne forwards towards the ventral aspect along the 

 outside of the origins of the shell muscles, and are gradually augmented by ad- 

 ditional muscular fibres arising from the cartilaginous framework, to which they 

 thus closely adhere. Having reached the ventral aspect of the body, they divide 

 into two tliick layers, both of which advance to meet their fellows at the mesial 

 line; the internal layers (i. fig. 2. pi. 3.) becoming blended together, embrace, as 

 it were, the shell muscles ; while the external layers (/. g. fig. 2. pi. 3.) diminish 

 to a thin edge, and overlap each other without becoming continuous ; and thus 

 is formed the commencement of the infundibular outlet, which gives passage to 

 the products of respiration and generation, and to the excrements. The canal 

 is then bent forwards, passes through the aperture in the mantle, and becomes 

 the external funnel described above. 



Besides the gradual augmentation in thickness which the sides or crura of the 

 funnel acquire from the fibres coming off" from the cephalic cartilage, they are 

 also strengthened by tolerably distinct fasciculi of longitudinal fibres (/t. fig. 2. 

 pi. 3.), which arise behind the terminations of the shell muscles, but in close 

 connexion with them, pass along the inside and near the posterior margins of 

 the crura of the funnel, and terminate at the base of the funnel. These fasciculi 

 are analogous to the more distinct rounded columns before alluded to, which 

 Cuvier has denominated, in Octopus, " les gros piliers laterals de I'entonnoir" 

 (e. e. fig. 1. & 2. pi. 1.), and which are also very distinct in Sepia and Loligo. 



D 2 



