ARTHROPODA. 



281 



those of the Argonaut and Poulpe are fixed. The Squid, 

 so much used for bait by cod-fishermen, has an internal 

 horny "pen," and the Cuttle has a spongy, calcareous 

 " bone." The extinct Belemnlte had a similar structure. 



FIG. 249 Paper Nautilus (Argonauta argo): 1, swimming towards a by ejecting wa- 

 ter from funnel, 6; 2, crawling on the bottom; 3, coiled within its shell, which is 

 one fourth natural size. Mediterranean. 



Squid have been found with a body seven feet and arms 

 twenty-four feet long, and parts of others still larger as 

 much as fifty feet in total length. 



Subkingdom VI. ARTHROPODA. 



This is larger than all the other subkingdoms put to- 

 gether, as it includes the animals with jointed legs, such 

 as Crabs and Insects. These differ widely from the Mol- 

 luscan type in having numerous segments, and in show- 

 ing a repetition of similar parts; and from the Worms 

 in having a definite number of segments and jointed 

 legs. 



The skeleton is outside, and consists of articulated seg- 

 ments or rings. The limbs, when present, are likewise 

 jointed and hollow. The jaws move from side to side. 

 The nervous system consists mainly of a double chain of 



