THE PAST AND PRESENT OF THE CUTTLEFISHES. 99 



lopment, it becomes a postulate of evolution that in them we should 

 find the cumulative increase and progress of their type. Thus 

 cuttlefish specialisation, so far from placing any difficulties in the 

 way of evolution, supplies additional proof of the growing applica- 

 bility of that doctrine to unravel the complexities of living structures. 

 Furthermore, as we advance from the older to newer types of cuttle- 

 fish life, the " skull" becomes better developed. It is better developed 

 in the two-gilled cuttlefishes, which are forms literally of the geological 

 yesterday, than in the pearly nautilus, which presents us with a cuttle- 

 fish type of vast antiquity. In the nautilus the skull consists of two 

 pieces, surrounding the gullet at its commencement ; but in the two- 

 gilled cuttlefishes it exhibits a middle portion, through which the 

 gullet passes, and likewise shows side-processes that form cavities or 

 " orbits," enclosing the eyes as in higher animals. Within this case 

 the three localised nerve-masses exist. Here, again, we discover that 

 in the later cuttlefishes the nervous axis is more concentrated than in 

 the earlier forms modification of, and progress in, structure accom- 

 panying development in time. A large nerve- mass, consisting of the 

 three closely connected centres, thus subserves the function of a 

 cuttlefish brain. Not the least interesting feature of this localised 

 mass of nervous matter is the fact that it exhibits the same arrange- 

 ment of grey and white nerve-matter that is seen in the highest brains. 

 An outer grey and an inner white layer are discernible in the nerve- 

 ganglia of cephalopods, as in the cerebrum of man ; and, as in the 

 highest animals, the cuttlefish grey matter is found to consist of nerve- 

 cells, whilst the white matter is chiefly composed of nerve-fibres. 

 Thus the laws of developmental progress affect the microscopic and 

 intimate structure of the living form as well as the more obvious 

 details of structure. From the main nerve-mass of the cuttlefishes 

 nerves arise to supply the body at large. Nerves of special sense 

 supply eyes, ears, and olfactory organs ; whilst the viscera and the 

 "mantle" or general body- covering are also well provided with the 

 means of innervation. 



Cuttlefish existence possesses in all probability the five "gate- 

 ways of knowledge," through which the impressions of the outer 

 world are received, and by which these impressions are modified 

 and transmitted to the brain-masses as sensations of sight, hearing, 

 smell, touch, and taste. There is little need to draw upon hypothesis 

 in the assumption that the arms or tentacles are efficient organs of 

 touch in Cephalopoda, or that the structures of the mouth may sub- 

 serve taste, in so far as the latter sense may be required to satisfy the 

 demands of cuttlefish existence. An organ of smell is definitely 

 situated behind or above the eyes. There, two small projections 

 or, as frequently, two minute pits or depressions, occur. These pits 

 are ciliated, and between the cilia " olfactory cells " are situated 



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