

122 ANIMAL KINGDOM. 



II. Worms. — Worm-like in form, consisting of many segments, with- 

 out any division into cephalo-thorax and abdomen ; the body fleshy ; 

 no jointed legs, though often furnished with tubercles, lamellae, or bris- 

 tles. Examples : the Earth-worm, Leech, Serpula. 



The aquatic species of Articulates commence in the Silurian, and 

 are here further explained. 



Crustaceans. — Among Crustaceans, there are three orders : — 



The first, or highest, ten-footed species, or Decapods ; as Crabs (Fig. 

 161) and Lobsters. 



The second, fourteen-footed species, or Tetradecapods (Figs. 162, 

 163, 164). 



The third and lowest, irregular in number of feet, and unlike the 

 Tetradecapods, also, in not having a series of appendages to the ab- 

 domen : the species are called Entomostracans, from the Greek for 

 insects with shells. 



(a.) Among the Decapods, Crabs are called Brachyurans, — from the Greek for short- 

 tailed, the abdomen being small and folded up under the body ; the Lobsters and 

 Shrimps, Macrurans, — from the Greek for long-tailed, the abdomen being rarely 

 shorter than the rest of the body. 



(b.) Among the Tetradecapods, Figs. 162, 164 represent species of the tribe of Isopods 

 (a word meaning equal-footed), and Fig. 163,of that of Amphipods (feet of two kinds, 

 abdominal as well as thoracic). Fig. 162 i9 the Sow-bug, common under stones and 

 dead logs in moist soil. Fig. 163 is the Sand-flea, abundant among the sea-weed thrown 

 up on a coast. In Figs. 162, 164 (Isopods), the abdomen is abruptly narrower than the 

 cephalothorax ; its appendages underneath are gills. In Fig. 163 (Amphipod), the ab- 

 domen is the part of the body following (usually) the eighth segment; its appendages 

 are swimming legs and stylets, — the gills in Amphipods being attached to the bases 

 of the true legs, and not to the abdomen. 



(c) Among Entomostracans, the forms are very various. The absence of a series of 

 abdominal appendages is the most persistent characteristic. The eyes, in a few species, 

 have a prominent cornea; but, in the most of them, the cornea is internal, and there is no 

 projection. In the Cyclops group, the species have often a shrimp-like form, as in Fig. 

 165, though usually minute. Sometimes the male and female differ much in form : 166 

 is male, and 165 female of the Sapphirina Iris; a bis the cephalothorax, and b d the 

 abdomen. There are legs on the under surface of the anterior part, fitted for grasping, 

 and others, behind these, for swimming. In the Cypris group, the animal is contained ' 

 in a bivalve shell, as in Fig. 168, and they are hence called Ostracoids. They are sel- 

 dom a quarter of an inch long. In the Limulus group, — containing the Horseshoe of 

 the sea-coasts of the United States, — there is a broad, shield-like shell, and a number 

 of stout legs, the basal joints of which serve for jaws. In the Phyllopod group, the 

 form is either shrimp-like, approaching Cyclops, or like Daphnia or Cypris; but the 

 appendages or legs are foliaceous and excessively numerous: the name is from the 

 Greek for leaf-like feet. In the Cirriped or Barnacle group, the animal has usually a 

 hard, calcareous shell, and it is permanently attached to some support, as in the Anatifa 

 (Fig. 169) and Barnacle. The animal opens a valve at the top of the shell, and throws 

 out its several pairs of jointed arms looking a little like a curl, and thus takes its 

 food, — whence the name, from the Latin cirrus, a curl, and pes, foot. The Anatifa 

 has a fleshy stem, while the ordinary Barnacle is fixed firmly by the shell to its sup- 

 port. 



Trilobites. — The Trihbites (Fig. 167, and also 251, and 360,448, 



