Cephalopoda — Tetralranchiata. 17 



TeutliidcB by Aristotle). This family not only embraces the largest Calama- 

 number of genera, but also those of the greatest size — the giants, ' 

 in fact, of the Molluscan kingdom. They have eight ordinary y^j^ 

 arms and two long tentacular arms, with expanded, club-shaped 

 extremities, which take their origin within the circle of the eight 

 ordinary arms, and are often six times as long. (Fig. 36.) 



In the genera Sepia, Sepiola, and Rossia these tentacles are 

 retractile, and can be withdrawn into two suborbicular pouches. 

 In Loligo and Sepioteuthis they can be partially drawn in ; in 

 Cheiroteuthis they are non-retractile. These tentacles, which are 

 armed with booklets or suckers at their extremities, are used, 

 like the lasso of the Indian, to seize their prey when at a distance. 

 The fossil booklets of several armed calamaries have been met 

 with in the Liassic and Oolitic formations, and many specimens 

 are exhibited. (See Fig. 33.) 



Squids and cuttles frequent the sea in numbers, and appear in 

 great shoals at certain seasons (probably for spawning) on the 

 coasts and banks both of Europe and America. They are 

 extremely alert and active in their movements, and, by means 

 of their pigment-cells (called chromatophores), they possess the 

 same power as does Octopus of changing the colour of their skin 

 to suit the surface of the bottom, or rocks on which they rest. 



Squids are taken in large numbers, for bait, by the fishermen 

 on the coast of Cornwall, with nets or lines. They are called 

 pen-and-ink fish, from the shape of their internal shell resembling 

 a quill pen in form, and from the readiness with which (when 

 alarmed) they discharge the inky fluid contained in their ink-bag. 

 These translucent horny ''pens" increase in number with age, 

 an old squid having as many as three or four enclosed within its 

 mantle, closely fitting together. The eggs are deposited in slender 

 sheaths, arranged in bunches like a mop, as many as 42,000 eggs 

 being found by computation in one bunch. 



One of the smallest known Cephalopods is the Sepiola Rondeletii. 

 This and an allied species do not exceed two to four inches in 

 length. The body is very short, and has two small, rounded, 

 lateral fins. (See Fig. 15.) 



2. — Teteabranchiata (four-gilled division). Cephalopods in 

 which the lateral margins of the mid-foot are inflected (but not 

 fused together), so as to form a funnel by apposition. The lobes of 



