98 STUDIES IN LIFE AND SENSE. 



to the wider instincts of cuttlefish existence. This process of nerve- 

 localisation and concentration is accompanied by certain important 

 modifications affecting other regions and structures of cuttlefish 

 economy. Thus the nerve-centres are found to be protected and 

 enclosed within a gristly or cartilaginous case, that foreshadows the 

 functions of the vertebrate skull, though in no sense connected with 

 that structure ; and the structure of the cuttlefish eye is likewise 

 peculiar, and presents a noteworthy feature of the economy of these 

 animals. Altogether, the disposition of the nervous axis presents us 

 with one of the most characteristic studies in cuttlefish history, and 

 offers at the same time, perhaps, more interesting problems in con- 

 nection with the evolution of the race than any other system of 

 organs included in the list of their bodily possessions. 



~ The first modification to which attention may be directed is the 

 massing of the nerve-centres around the gullet in the cuttlefishes. 

 Gathered up, as it were, from the foot and viscera, we find the chief 

 nervous masses disposed within the head region, and further enclosed 

 within the cartilaginous case or " skull " already mentioned. This 

 concentration of nerve-masses in the cephalic or head region is in 

 itself noteworthy. It teaches us that the tendency to " cephalisa- 

 tion," as Professor Dana has termed the process of head-develop- 

 ment, is largely associated with, if not directly induced by, this 

 nervous concentration ; and it likewise reveals one of the main 

 causes of superiority and advance in the animal series. But the 

 presence in the head of the cuttlefishes of the cartilaginous " skull," 

 in addition to sundry other masses of gristle scattered through the 

 substance of the " mantle," has just been mentioned as a feature of 

 interest. No possible lines of connection, genetic or otherwise, 

 exist between cuttlefishes and vertebrates ; yet this " skull " cha- 

 racter would at first sight seem to indicate resemblance and relation- 

 ship of a definite kind between the two groups. But the case before 

 us merely adds one to already known instances in which structures 

 of analogous or similar nature have originated in a perfectly inde- 

 pendent fashion. Such a result, however, does not, as has been 

 argued, lie outside those normal laws of progressive development 

 through the operation of which the universe of life has become the 

 wondrously complex thing it is. The vertebrates themselves exhibit 

 a progress of skull development leading us from that skull-less, 

 spineless, boneless fish the lancelet (Amphioxus], through the im- 

 perfectly differentiated crania of the lampreys and their allies, to the 

 complex skulls of our common fishes, and upwards by diverging 

 lines to crania of higher type still. Is it any the more anomalous to 

 find in the cuttlefishes the progressive development of a protective 

 case for the modified and concentrated nerve-centres? Considering 

 that the cephalopods stand at the extreme limit of molluscan deve- 



