243 



CHAP. XIII. 



CRUSTACEA. 



CRABS— LOBSTERS. 



How are they distinguished from the Insects ? — Barnacles and Acorn-shells.— 

 Siphonostomata. — Entomostraca. — King-Crab. — Edriophthalmia.— Sandhoppers. 

 — Thoracostraca. — Compound Eye of the higher Crustaceans. — Respiratory 

 Apparatus of the Decapods. — Digestive Organs. — Chelae or Pincers. — Distribu- 

 tion of Crabs. — Land Crabs The Calling Crab. — Modifications of the Legs in 



different species. — The Pinna and Pinnotheres. — Hermit Crabs. — The Lobster. 

 — The Cocoa-nut Crab. — The Shrimp. — Moulting Process. — Metamorphoses of 

 Crabs. — Victims and Enemies of the Crustaceans — Their Fecundity. — Marine- 

 Spiders and Insects. 



The Crustaceans were included by Linnaeus among his insects, 

 but their internal structure presents such numerous and im- 

 portant differences that modern naturalists have raised them to 

 the dignity of a separate class. They have indeed, in common 

 with the insects, an articulated body, generally cased with hard 

 materials ; they are like them provided with jointed legs, with 

 antennae or feelers, and their organs of mastication are similarly 

 formed ; but insects breathe atmospheric air through lateral 

 pores or tracheae, while the crustaceans, being either aquatic 

 animals or constantly frequenting very damp places, have a 

 branchial or a tegumentary respiration. The perfect insect 

 undergoes no further change ; the crustacean, on the contrary, 

 increases in size with every successive year. The higher crus- 

 tacean possesses a heart, which propels the blood, after it has 

 been aerated in the gills, to every part of the body ; in the insect 

 the circulation of the blood is by no means so highly organised. 

 On the other hand many of the insects are far superior in point 

 of intelligence to even the best endowed crustaceans, for here 

 we find no parental care, no mutual affection, no joint labours 

 for the welfare of a large community, no traces of an amiable 



