THE AGE OF LNVERTEHRATES OF Tlir: SEA. 7' ' 



the case of the ordinary bivalves, however, the modern (ias- 

 tropods much exceed in numbers and magnitude those of the 

 J'alceozoic. 



The highest group of MoUusks, represented in the modern 

 ocean by the Nautili and Cuttle-fishes, has a history so strange 

 and eventful, and so different from what might have been 

 anticipated, that it perhaps deserves a more detailed notice, 

 more especially as Uarrande has recently directed marked 

 attention to it in his magnificent work on the Palaeontology 

 of Bohemia. 



The Cuttle-fishes and Squids and their allies are, in the 

 modern seas, a most important group (Fig. 64). The great 

 numbers in which the smaller species appear on many coasts, 

 and the immense size and formidable character of others ; 

 their singular apparatus of arms, bearing suckers, their strange 

 forms, and the inky secretion with which they can darken the 

 water, have at all times attracted poi)ular attention. The 

 great comjjlexity of their structures, and the fact that in many 

 points they stand (juite at the head of the invertebrates of the 

 sea, and approach most nearly to the elevation of the true 

 fishes, liavc secured to them the attention of naturalists. Some 

 of these animals have shelly internal supports, and one genus, 

 that of the Argonauts, or Paper Nautili, has an external pro- 

 tective shell. Allied, though more distantly, to the cuttle- 

 fishes, are the true Nautili, represented in the modern sea 

 principally by the Pearly Nautilus, though there are two other 

 species, both of them very rare. The modern pearly nautilus 

 (Fig. 65) may be regarded as a peculiar kind of cuttle-fish 

 ])rovided with a discoidal shell for protection, and also for 

 floatage. The shell is divided into a number of chambers 

 by partitions. Of these the animal inhabits the last and 

 largest. The others are empty, and are connected with the 

 body of the animal only by a ]npe, or siphuncle, with mem- 

 branous walls and filled with fluid. Thus provided, the 

 nautilus, when in the water, has pradi'ally no weight, and (an 



