392 NATURAL ARRANGEMENT OF INSECTS. 



ing Crustacea we find so frequently in stagnant waters, 

 such as Talitrus, Gammarus, Phronime, Sec. ; the 

 Crustacea Lcumodipoda contains Cyamus, &c., which 

 live as parasites upon the whale, and others, as Caprel/a, 

 are %vanderers ; the Crustacea Isopoda are broad 

 and depressed, and do not leap : among these we find 

 Oniscus, or the woodlice; the Cymotho'e, which are para- 

 sites, and very broad ; and Idotea, which are equally 

 slender. To this division, the fossil Trilohites very 

 closely approach in general structure. 



(355.) The Entomostraca form the last division of 

 the Crustacea. In these are the Branchiopodes, con- 

 taining the remarkable forms of Monoculos, or Cyclops, 

 which are very minute and pyriform insects ; Zoe, with 

 its digitated legs ; Apus, with its case covering its 

 body. It is here, doubtlessly, that the extraordinary 

 form of Limulus should come : these are large creatures 

 sometimes two feet long, and peculiar to the seas of 

 America and India ; specimens frequently occur in Chi- 

 nese boxes of insects ; they have a large hemispherical 

 crust covering the anterior portion of the body, and a 

 long and slender tail : and lastly, the Pcecilopoda, which 

 comprise the only truly suctorial Crustacea ; among 

 which there have been observed, in their early stages, con- 

 siderable transformations. They live chiefly as parasites 

 upon other animals, and especially fishes. Amongst them, 

 Argulus has natatorial legs, and Cecrops is short and 

 stout, without legs; and Dichelestion, which is parasitical 

 upon the sturgeon, is long and slender. Naturalists have 

 not fully determined where the Pycnogonidcc should 

 be placed, — Avhether proximate to Phalangium among 

 the ArachnidcB, or with the Crustacea, linking the two 

 orders : Latreille adopts the former view ; but Walcke- 

 naer and Milne Edwards, respectively the greatest au- 

 thorities in their two branches of Arachneology and 

 Crustaceology, concur in considering them crustaceous. 

 They are spider-looking creatures, with eight very long 

 and ungulated legs ; but, in addition to these, the females 

 have two pseudo legs for carrying their eggs. They are 

 occasionally found upon the Cetacea, upon which they 



