cartilage its two narrow posterior blade-like projections (<L same 



Hi:.). '" ''"' genus Cirroteuthis, an anomalous Octopod of which 



only a single species is known, the dorsal cartilage is very broad. 

 -i. a- li simulate the internal shell or pen of the decapod. A 1. 

 the entrance of the anterior ventral mantle opening is found a 

 singular call ilaginous mechanism, which d'Orbigny has called 

 the "apparcil de resistance," peculiar to the cephalopoda, which 

 consists of buttons Or ridges and corresponding grooves placed 

 on 1 he opposed inner side, of the mantle and the body, and by 

 which the animal may at will button its head to the mantle to 

 prevent the injury which might otherwise result to it during a 

 si niggle with wave or prey, in consequence of its want of support 



there (Plate 1. I'm". '2). On the other hand, by relaxing this sup- 

 port the animal preserves for itself a freedom of movement of 

 head and arms which would be impracticable were these as per- 

 manently and closely connected with the body on the ventral as 

 they MIV on tin 1 dorsal side. The arrangement of this resisting 

 apparatus varies in different genera, and is a good distinctive 

 cliMrictcr. Largely developed in those species which have no 

 fixed attachment, to the body, as in Ommastrephcs, Loligo. etc.. 

 it exists also in those genera which possess only a very small 

 cervical baud of attachment, as in Argonauta. but it is wanting 

 in those genera in which the permanent bands arc well-developed. 

 M in < >ctopus. ( Yalichia, etc. 



In I'hiloncxis or Tremoctopus, a button is found at the base 

 of the siphon tube, with a corresponding groove to receive if 

 upon the inner wall of the mantle, but in Argonauta the relative 

 position of button and buttonhole is reversed. In Kossia we find 

 a short ridge surmounted by a profound groove opposed to an 

 elongated groove on the base of the siphon ; in Loligo and Scpi- 

 oteiiihix (lig. L>) the ridge is somewhat longer, without groove-: 

 in Onyclioteuthis and Knoploteiit his the ridge is nearly half the 

 length of the body, with the siphonal groove; in Sepia an oblique 

 blong button can be tixed into a similarly formed pit upon the 

 siphon: in < 'hiroteut his t here are an oblong longit udinal button 

 and two lateral pits fitting into a cent nil pit and two buttons on 

 tin* siphon: finally, in Ommasircphcs. in which it is most com- 

 plicated, there are two projections, one oblong and the other 

 triangular, entering cavities upon t he^siphonal tube, and two 



