604 CEPHALOPODA. 



imperfect Sepia. This communication, which in vertebrate animals is 

 invariably effected through an opening in the walls of the abdomen, 

 whereby the vitelline duct penetrates to the alimentary canal, here oc- 



Fig. 303. 



1234 



Embryo of Cuttle-fish. 



cupies a very unusual situation, being inserted into the head, through 

 which it penetrates, by an aperture situated in the front of the mouth, 

 to the oesophagus, where it terminates (fig. 303, 3). 



(1611.) Among the many interesting phenomena presented by the 

 CEPHALOPODA, few are more remarkable than the extraordinary power 

 which these animals possess of continually changing their colour in con- 

 formity with the varying tints of surrounding objects, affording a means 

 of defence almost as efficient for concealment as the ejaculation of their 

 inky fluid. It is indeed an extremely beautiful sight to witness the 

 flickering hues of one of these animals, that seem to succeed each other 

 with astonishing rapidity. In order to explain the cause of this very 

 curious faculty, it is only necessary to examine with the microscope a 

 portion of integument removed from the living animal, when it becomes 

 at once apparent that the coloured layer of the skin is studded with 

 innumerable pigment-cells (chromatojphores), filled with colours that 

 exactly correspond with the hues of the creature's body, and which in- 

 dividually possess a remarkable power of changing their shape and size, 

 and thus modifying, by their contraction and expansion, the coloration 

 of the integument*. 



(1612.) Interesting as the subject is, our space will permit us to ad- 

 vert but very briefly to the important light which our comparatively 

 recently acquired knowledge of the anatomy of the Cephalopod Mollusca 

 has thrown upon the history of innumerable races of similarly con- 

 structed beings long extinct, the remains of which are extensively 

 distributed through a variety of geological strata. The fossil Ammonites 

 for example, the nature of which was previously inexplicable, were at 

 once rendered intelligible by the discovery and description of the Nau- 



* This wonderful faculty of changing their colours, dependent on a similar organi- 

 zation of the rete mucosum, is possessed by fishes, frogs, and many other animals, as 

 may be demonstrated by simply placing a few small trouts, gudgeons, or minnows 

 in differently coloured earthen pans filled with clear water ; and the phenomenon is 

 rendered still more conspicuous by suddenly transferring them from the lighter to 

 the darker coloured vessels, and vice versa. 



