THE PAST AND PRESENT OF CUTTLE-FISHES. 761 



running in parallel, but nevertheless in distinct and independent, lines; 

 and this likeness is further strengthened when we discover that not 

 merely the ear, but the eye likewise, of these two groups of animals 

 is formed or developed in an essentially similar fashion. The ear of 

 the cuttle-fish presents us with a permanent example of an early and 

 transitory stage in the development of the vertebrate ear, and a com- 

 mon plan of ear-production is thus seen to traverse a wide extent of 

 the animal world. 



"The present history of the cuttle-fishes may be concluded by the 

 briefest possible reference to their distribution and classification. 

 Over two thousand species of cephalopods are known. But geology 

 claims the vast majority, only two hundred and eighteen 6pecies being 

 included in the ranks of living animals. The cuttle-fishes are very 

 widely distributed in existing seas. They occur in the far north ; 

 they are plentifully represented in the colder seas by the squids which 

 form the bait of the Newfoundland cod-fishers; but in tropical regions 

 they attain their greatest size and numerical strength. Their classifi- 

 cation is both simple and natural. Their division into Dibranchiates 

 (" two-gilled ") and Tetrabranchiates (" four-gilled ") is a method of 

 arrangement which accurately reflects variations in their existing 

 structure, as it correctly indicates the main lines of their geological 

 and past history. Of four-gilled cuttle-fishes there is but one living 

 example the pearly nautilus (Fig. 3). Its special and distinctive 

 peculiarities may be rapidly summed up in the statement that it has 



Fig. 3. Pearly Nautilus. 



four gills, numerous arms (c), no suckers, no ink-sac, an incompletely 

 tubular funnel (f), stalked eyes, and an external, many-chambered 

 shell, in the last formed and largest compartment (e) of which the 

 body is lodged. 



The absence of| an ink-sac in the nautilus is a fact correlated with 

 its bottom-living habits and with the absence of any need or require- 



