Monograph of tJie Crudcicea of the Cincinnati Group. Ill 



anchylosetl into the apparently undivided head or thorax of many 

 groups. In the majority of Crustacea the first seven joints belong to 

 the head, and bear the organs of sense and parts of the mouth, the 

 next seven t^? the thorax (according to ]M. Edwards), bearing the or- 

 gans of locomotion ; this last thoracic joint being always defined by 

 the male sexual openings, and the last seven to the abdomen contain- 

 ing the principal viscera, and having the anus in the last joint. The 

 first ring bears the eyes when they are present, the second and third 

 rings bear the two pair of antenna, which are absent only in the low- 

 est types, the fourth bears the mandibles, the fifth and sixth the jaws, 

 the appendages of the succeeding rings varying in shape and use ac- 

 cording to the group. Digestion : the complex mouth is always on the 

 under side of the head, composed of the lahrum or upper lip, a labium 

 or under lip, jau--feet, mandibles, maxilke, palpi, etc., which it is unne- 

 cessary to describe, followed by a short, vertical cesophagus, leading to a 

 large, globular stomach, directly over the mouth (often containing sharp 

 tubercles for triturating the food), from which, as in all the annulata, 

 a straight intestine leads to the anus ; there is a well developed liver. 

 Circulation by a well developed heart, placed befiind the stomach, of 

 mixed blood, which imbibes the chyle from the intestines. Respira- 

 tion, in the higher groups, by gills, w^hich are modifications of the 

 flabelliform appendage of certain legs : in the lowest, apparently by 

 the whole surface of the body, without special organs. Nervous system, 

 on the plan of the subkingdom Aniiculata. Hearing : the higher 

 groups hear well, the ear being situated in the base of the second pair 

 of antenna. Sight: a few parasitic groups are blind in their perfect 

 state, but nearly all the rest have perfect eyes, either simple or semi- 

 compound. The simple eyes are small, two or three in number, of a 

 single set of lenses, each eye covered by a round, smooth cornea ; tlie 

 semi-compound eyes are an agglomeration of simple eyes, each with its 

 set of lenses and separate twig of optic nerve, the group of eyes covered 

 by one simple, smooth, external cornea (true compound eyes, having a 

 separate facet of the outer cornea for each eye beneath). Reproduc- 

 tion : sexes alwavs distinct and in different individuals. 



" The class Crustacea is naturally divisible into the five following or- 

 ders, commencing with the lowest in organization : 1st, Cir)~ipedia, or 

 Barnacles ; 2d, Suctoria, or the little, parasitic Crustacea with tubular 

 mouths; Sd, Entomostraca ; -ith, Edriophthalma; oth, Podophthalrna, or 

 most highly organized and having pedunculated eyes (crabs, lobsters, 

 etc.) 



Third Order — Entomostraca. 

 The little Crustacea which compose this order are very variable in 



