i88 CRUSTACEA. PART m. 



SECTION YIL 



THE CRUSTACEA. 



THE Crustacea are free, locomotive, articulated ani- 

 mals, covered with a crust or external skeleton, and dis- 

 tinguished by having jointed limbs, and gills that fit 

 them for aquatic respiration. They are male and female, 

 and, though extremely diversified, they have a similarity 

 in their general structure. Many are microscopic. 



The Crustacea constitute ten orders, many genera, 

 and innumerable species. The Decapods, or the ten- 

 footed order, are by far the most complicated in organi- 

 zation. They have prominent eyes, movable on jointed 

 stalks, antennse, gills in a cavity on each side of the 

 throat, a mouth opening into a digesting apparatus, a 

 heart, liver, circulation of the blood, and a nervous sys- 

 tem, and are therefore animals of a higher grade than 

 any that have come under consideration. 



The Decapods are divided into three tribes : the 

 Macrura, or long-tailed Crustacea, of which the Lob- 

 ster and Astacus fluviatilis, or fresh-water Crawfish, are 

 types ; the Anomura, or tailless tribe, of which the Her- 

 mit crab is the type ; and the Brachyura, or short-tailed 

 crustaceans, which are represented by the common Crab. 

 The greater number of these animals are marine ; some 

 inhabit fresh water ; and some are amphibious, living in 

 holes in the ground ; others climb reeds and bushes with 

 their long claw-feet ; the last two kinds come to water 

 to spawn. 



