xxvi INTRODUCTION. 



moveable segments and feet, as the Earwig and Scolopen- 

 dra ; next the innumerable tribes of Insects, most of which 

 feed on plants, but many of which are predaceous ; next the 

 Arachnida, comprehending the Spiders and Scorpions, crea- 

 tures strong, voracious, and endowed with wonderful in- 

 stincts, and frequently supplied with poison to destroy their 

 prey, or with secretions to form nets for entangling it ; and, 

 lastly, are the Crustacea, as the Lobster and Crab, having a 

 horny skeleton, enveloping the softer parts, and formed with 

 articulations or joints, to allow of the requisite freedom of 

 motion. 



The Mollusca differ from the Articulata in not having 

 jointed bodies and limbs, but a soft body, covered by a mus- 

 cular integument, which assumes various forms in the differ- 

 ent tribes, and in most of them gives out a calcareous secre- 

 tion, which, hardening, forms a shell to serve for the pro- 

 tection of the animal. They are aquatic, with the exception 

 of a few tribes. They are infinitely diversified in size and 

 form ; but they are generally either slow-moving or fixed to 

 a spot, as the Oyster, the Mussel, and other animals termed 

 shell-fish. There are many of them phosphorescent, and 

 emit a brilliant light. They abounded in the past ages of 

 the world ; and whole mountains, and immense calcareous 

 strata, are formed of their remains. The lowest in the scale 

 are those which are soft, without heads, and destitute of cal- 

 careous secretion without or within the body : the next are 

 those which have shells, but are without heads, though fur- 

 nished with mouths, and numerous eyes around the mar- 

 gins of their integument: the next are those which have 

 shells, and a muscular disc extended under the abdomen, and 

 serving like a foot for crawling along the surface : the next 

 are those which are especially adapted for swimming, and 

 are either with or without a shell : the last and highest in 

 the scale are those which have feet and arms disposed around 

 the head, and which are, many of them, powerful beasts 

 of prey, furnished with large tentacula with which they 



