CARTILAGES. 61 



The cartilages of the hack and of the fins are shown in position 

 in Plate liii, 47, after Keferstein, of Sepia officinalis. In the 

 Loligos the moon-shaped cartilage of the back is wanting, bnt is 

 replaced in its functions by the upper end of the corneous pen 

 or inner shell. In the octopods there remain only of this back- 

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

 fig.). In the genus Cirroteuthis (iv, 58), the dorsal cartilage is 

 verj^ broad, so as 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 sides 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 pi'ey, in consequence of its want of 

 support there (iv, 51). On the other hand, by relaxing this 

 support the animal preserves for itself a freedom of movement 

 of head and arms which would be impracticable were these as 

 permaneutl}^ and closely connected with the body on the ventral 

 as they are on the dorsal side. The arrangement of this resisting 

 apparatus varies in difl"erent 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 yery 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, Cranchia, 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 Rossia we 

 find a short ridge surmounted by a profound groove opposed to 

 an elongated groove on the base of the siphon ; in Loligo and 

 Sepioteuthis, the ridge is somewhat longer, without grooves ; 

 in Onychoteuthis and Enoploteuthis the ridge is nearly 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 Chiroteuthis there are an oblong longitud- 

 inal bu.tton and two lateral pits fitting into a central pit and two 

 buttons on the siphon ; finally, in Ommastrephes, in which it is 

 most complicated, there are two projections, one oblong and the 

 other triangular, entering cavities upon the siphonal tube, and 

 two projections upon the latter which enter between the tubercles 

 of the opposed mantle. The complexity of this attachment 

 increases, it will be perceived, with the activity of the animal. 



