122 / ANIMAL KINGDOM. 



3. 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, Intestinal Worm. 



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 Brachyurarts, — from the Greek for short- 

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

 Shrimps, Maerurans, — 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 is 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 b is 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 Trilobites (Fig. 167, and also 251, and 360, 448),. 



