Introduction. xvii 



4. Acephala, or Headless Mollusca. These animals have no apparent 



head, and breathe by means of branchiae, which are generally 

 ribbon-shaped. Most of them are enclosed in a bivalve shell, 

 but some are naked ; the former are the Testacea of Cuvier, and 

 the Conchifera of Lamarck ; the latter are the Tunicata of 

 Lamarck. They form two orders. 



5. Brachiopoda, or Arm-footed Mollusca, These animals also have a 



bivalve shell ; but they have no true branchiae, and their respi- 

 ration is effected by the agency of the mantle. They have two 

 spiral arms. 



6. Cirrhopoda, or Curled-footed Mollusca. These are generally attached, 



and enclosed in a shell of several pieces ; they are furnished 

 with a mouth, armed with jaws, and with several pairs of jointed 

 and fringed organs, called cirri, by the protrusion and retraction 

 of which they capture their prey. Examples of this class are 

 the Barnacles and Acorn shells. These animals have long 

 ceased to be regarded as Mollusca, the investigations of modern 

 naturalists having proved them to be true articulated animals 

 most nearly related to the Crustacea. 



THE AKTICULATED ANIMALS 



Have no back-bone. The covering of the body is sometimes hard and 

 sometimes soft, but it is always divided into segments by a number of 

 transverse incisions. The limbs, when the body is provided with any, 

 are jointed ; and they can be separated from the body without any 

 serious injury being sustained by the animal, new limbs being shortly 

 after formed to replace them. The senses of tasting and seeing are 

 more perfect than those of the Mollusca, though that of feeling seems 

 much less acute. In other respects the four classes differ considerably 

 from each other. 



[ The Entozoa, or Intestinal Worms, placed by Cuvier and others 

 among the Radiata, are now arranged amongst the lowest forms of 

 articulated animals, as are also those animalcules known as Botifera.~] 



\. The Annelida, or Red-Hooded Worms, have no heart, properly so 

 called, but have sometimes one or more fleshy ventricles. They 

 breathe through branchiae. Their bodies are soft, and more or 

 less elongated, being divided into numerous rings or segments. 

 The head, which is at one extremity of the body, can scarcely 

 be distinguished from the tail, except by having a mouth. These 

 animals have no feet, properly so called, but they are furnished 

 with little fleshy projections, bearing tufts of hairs or bristles, 

 which enable them to move. They are generally of carnivorous 

 habits. They lay eggs, but the young are frequently hatched 

 before exclusion, and hence these creatures are said to be ovo- 

 viviparous. Their study is called Helminthology. As examples 

 of the three orders of this class may be mentioned the serpulee 

 or worm-like animals, often found on shells, the common earth- 

 worm, and the leech family. 



II. Tlie Crustacea comprise the shell-fish commonly called crabs, 

 lobsters, shrimps, and prawns. They have a distinct head, fur- 

 nished with antenrice, eyes, and mouth ; and their bodies are 



