8 CARTILAGES. 



cartilage its two narrow postericM- l>hulf-like iirojections (rf, same 

 fig.). In the genus Cirroteuthis. an anomalous Octopod of which 

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

 so as to simulate the internal shell or pen of the decai)od. At 

 the entrance of the anterior ventral mantle opening is found a 

 singular cartiloginous mechanism, which d'Orhigny has called 

 the '•api)areil de re'sistance," peculiar to the cephalopoda, which 

 consists of buttons or ridges and corresponding grooves [)laced 

 on the oi)posed inner side of the numtle 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 

 struggle with wave or prey, in consequence of its want of support 

 there (Plate 1, fig. 2). On the other hand, by relaxing this sup- 

 port the animal i)reserves for itself a freedom of movement of 

 head and arms which would be impracticable were these as })er- 

 manently and closeh' connected with the body on the ventral as 

 they are on the doi'sal side. The arrangement of this resisting 

 apparatus varies in different genera, and is a good distinctiA'c 

 character. Largeh^ developed in those species which have no 

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

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

 cervical band of attachment, as in Argonauta, but it is wanting 

 in those genera in which the permanent bands are well-developed, 

 as in Octoi)us, Cranchia, etc. 



In Philonexis or Tremoctopus, a button is found at the base 

 of tile siphon tube, with a corresj)onding groove to receive it 

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

 l)osition of button and buttonhole is reA^ersed. In Rossiawe find 

 a short ridge surmounted by a profound groove opposed to an 

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

 oteuthis (fig. 2) the ridge is somewhat longer, without grooves ; 

 in Onychoteuthis and Enoi)loteuthis the ridge is nearly half the 

 length of the body, with tlie siphonal groove ; in Sepia an obli(iue 

 oblong button can be fixed into a similarl}- formed pit upon the 

 siphon ; in Chiroteuthis there are an oblong longitudinal button 

 and two lateral pits fitting into a central pit and two buttons on 

 the siphon ; finally, in Ommastrephes, in which it is most com- 

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

 triangular, entering cavities upon the siphonal tube, and two 



