( 477 ) 



CHAPTEE XVII. 



THE CRUSTACEA. 



" Multa tamen Isetus tristia pontus habet." 



OVID. 



THE animals of this class, as regards organisation, must be placed 

 higher in the scale than the Arachnidae, or spiders ; hut they are 

 beneath the Mollusca, although as regards affinity, the Mollusca in 

 their lower division the Molluscoida more approximate to the Polyp 

 class than, to the Crustacea. 



The Crustacea is the highest division of articulate- animals with feet ; 

 they breathe by means of gills, and have no stigmata, or air-passages, 

 as in insects. The name signifies a hard crust or covering, with 

 which the animals are protected. This consists of layers of carbonate 

 of lime with one of pigment, generally, but not always, on the surface. 

 The general outline of these animals is peculiar ; unlike insects, they 

 are not divisible into head,. thorax, and abdomen; many species truly 

 have no head at all ; but a pair of eyes point to the seat of intelligence. 

 Most of these animals have two compound eyes ; but a few, like some 

 insects, have both simple and compound eyes. The mouth is situated 

 in the under part of the anterior of the body : in some cases they have 

 jaws, as in crabs ; in others suckers only. 



Passing over the vast numbers of beings which inhabit the debatable 

 ground the Annelids, which were for ages confounded with the worms, 

 because of their resemblance in form; a form which might be declared 

 forbidding, but, as Aristotle has well said, Nature, in her domain, 

 knows nothing low, nothing contemptible ; the sea-leeches, whose con- 

 dition was an impenetrable mystery to Pliny, " Omnia incerta ratione, 

 et in naturae majestate abdita ;" and the singular cirripedes, one species 

 of which, the barnacle (Anatifa Itevis), was thought by old Gerard, 



