N CAKTILAUKS. 



cartilage its two narrow posterior blade-like projections (c/, same 

 lig.). In the genus Cirroteuthis, an anomalous Octopod of which 

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

 so MS to simulate the internal shell or pen of the decapod. At 

 the entrance of the anterior ventral mantle opening is found a 

 singular cartilaginous mechanism, which d'Orbigny has called 

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

 consists of buttons or ridges and corresponding grooves placed 

 on the 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 

 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 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 are on the dorsal side. The arrangement of this resisting 

 apparatus varies in different genera, and is a good distinctive 

 character. Largely 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 Octopus, Crane hia, etc. 



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

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

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

 position of button and buttonhole is reversed. In Kossiawe 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 (lig. 2) the ridge is somewhat longer, without grooves; 

 in Onychoteuthis and Knoploteuthis the ridge is nearty half the 

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

 oblong button can be fixed into a similarly formed pit upon the 

 siphon ; in rhiroteuthis there are an oblong longitudinal button 

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

 the siphon; Dually, in Oimiiastrephes, 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 



