86 STUDIES IN LIFE AND SENSE. 



position as "molluscs," and the Lamellibranchs, gasteropods, and 

 cuttlefishes therefore remain in close structural and developmental 

 relationship to represent the molluscan branch of the great genea- 

 logical tree of the animal world. It is most important, at the outset 

 of our study, to bear clearly in mind the systematic position of the 

 cuttlefishes in the series. Their apparently marked affinities in 

 several respects with vertebrated animals might lead to the supposi- 

 tion that the cuttlefishes possessed a relationship with the highest 

 type of animals. But, as we shall hereafter note, such likenesses are 

 explicable on other grounds than that of a common origin. Standing 

 at the far extremity of a " phylum " or branch of the animal series, 

 the cuttlefishes possess neither structural nor other direct affinity 

 with the vertebrates, whose root-stock, lying in the tunicate group, 

 has but the remotest affinity with the beginnings of molluscan 

 development. In a word, the Cephalopoda exist in that most natural 

 classification of animals, which, as Darwin remarks, is the embryo- 

 logical or developmental, at the tip of one branch of the animal tree. 

 The vertebrates, on the other hand, have developed along a different 

 and widely divergent branch, whose lines of growth are in nowise 

 parallel to, and attain a far higher rank than, those of the molluscan 

 twig. The mere consideration of the relative position of the cuttle- 

 fishes in the series thus impresses the all-important truth, that the 

 classification of living beings can in no sense be represented by the 

 linear arrangement of former scientific periods. The constitution of 

 both animal and plant worlds is not that of simple even growth in 

 one direction ; nor does each round of the ladder fall into its natural 

 place as beneath a higher and above a lower group respectively. We 

 cannot in nature begin with the monad, and advance by successive 

 stages in a straight line through every known form, upwards and 

 onwards, to man. The natural arrangement of animals or plants is 

 that indicated by their development. The groups of living beings 

 are the divergent branches of a tree ; all of which branches have 

 something in common with the parent stem, but present us with 

 divergent lines of growth and with wide variations in the height or 

 rank to which they attain. 



The definition of the Cephalopoda, or cuttlefish class, is largely a 

 matter of commonplace observation. Linnaeus, naming them " cepha- 

 lopods," or " head-footed " molluscs, indicated the structural feature 

 which was calculated to appeal most plainly even to non-technical 

 minds. The circlet of arms, feet, or tentacles crowning the head- 

 extremity of a cuttlefish, thus presents us with a personal character 

 of unmistakable nature. It is necessary, however, to bear in mind 

 that the ordinary and to a certain extent natural fashion of represent- 

 ing a cuttlefish head upwards is, in zoological eyes, a complete 

 reversion of its surfaces. To understand clearly why to speak of a 



