312 



MOLLUSCA 



[CH. 



the English Channel and also abundant in the Mediterranean, where 

 it is a favourite article of food ; Moschites cirrosa with eight arras 

 and a single row of suckers ; Polypus (or Octopus') vulgaris almost 

 confined to the south coast and commoner on the French shores 

 and in the Mediterranean. Another Squid, Ommatostrephes, is 

 common in the Gulf of St Lawrence and on the shores of the eastern 

 United States. 



The body of Sepia appears to be composed of a swollen head 



separated by a neck from 



I ~ \^^^C^) a tapering trunk. When 



closely examined, however, 

 the body is seen to be no- 

 thing but a long pointed 

 visceral hump, like that of 

 the snail, but it is not 

 ^^^^ twisted and is not protected 



"""^ by an external shell. The 



mantle, as in the snail, is a 

 skirt-like fringe of skin, the 

 space between its inner 

 surface and the visceral 

 hump forming the large 

 mantle-cavity. In order 

 to compare the animal 

 with the snail it must be 

 placed with the point of 

 the hump projecting up- 



i-'' / x 1 / wards and backwards 



(Fig. 142). The so-called 

 head includes the true 

 head, with two enormous 

 eyes of almost human 



2 



III 



-~3 



'-/- 2 



FIG. 142. Diagrams of a series of Molluscs 



to show the form of the foot and its 



regions and the relations of the visceral 



hump to the antero-posterior and dorso- 



ventral axes. After Lankester. 

 I. A Prosobranch Gastropod. II. La- 



mellibranch. III. A Cephalopod. 



A. Anterior surface. P. Posterior sur- 

 face. D. Dorsal surface. V. Ventral 



surface. 1. Mouth. 2. Anus. 



3. Mantle-cavity. 4. Foot. 



covered on their inner sides with stalked suckers (Fig. 143), and 

 two very long arms bearing suckers only at their expanded ends. 

 These latter can be pulled back into two large pits situated at their 

 bases, and when so retracted they are completely hidden from view. 

 The sucker is a cup with a horny rim which keeps the opening 

 from collapsing. In its base there is a swelling, which is the end 



aspect, surrounded by the 

 fore-foot. The fore-foot 

 is drawn out into eight 

 short pointed arms, thickly 



