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 Belemnite had a similar structure. 
Fio. 249.—Paper Nautilus (Argonauta argo ): 1, swimming towards a by ejecting wa¬ 
ter from funnel, b; 2, crawling on the bottom; 3, coiled within its shell, which is 
oue 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 witli 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 
