INTRODUCTION". IX 



head, viz., the antenna, the antennules, and the eyes. The 

 second pair of maxillae much resemble the first pair of maxilli- 

 pedes in general appearance, the coxopodite and basipodite are 

 produced inwards in the form of deeply bilobed lamellae fringed 

 internally with short hairs ; the ischium forms a short process 

 internal to this the other joints being undeveloped ; the exo- 

 podite and epipodite combine to form a broad plate the 

 scaphognathite which lies in the cervical fold, and during life is 

 constantly in motion, scooping the water out of the branchial 

 cavity, and thus causing a constant current to flow over the gills. 

 The first pair of maxillae consist of three parts two thick 

 internal plates, bordered with stout bristles, and representing 

 probably the coxopodite and the basipodite, and an external 

 palpiform appendage provided at the end with a few longish 

 hairs. The mandibles consist of two parts a thick hard body, 

 obscurely toothed internally, and a large leaf-like appendage. 

 The sternum of the segment bearing the mandibles is called the 

 endostome or palate. In front of the mandibles and overhanging 

 the mouth is a fleshy median prominence the labritm. In front 

 of the orifice of the mouth (buccal orifice) is a flat space, not 

 very wide in the Prawn, and hidden by the appendages of the 

 mandibles, which corresponds to the sternum of the next pre- 

 ceding or antennary somite, and is termed the epistome. 



The antennce (or external antennce as they are frequently termed 

 by systematists in contradistinction to the internal antennce 

 or antennules) consist of a short basal joint the coxicerite, 

 on which is situated the orifice of the "green gland," or supposed 

 renal organ ; a second, broad and short joint, the basioerite, to 

 which is articulated externally the scaphicerite, squame, or 

 exopodite of the antennae an elongate scale ; a third, fourth, 

 and fifth joints, narrower than the preceding, and called 

 respectively the ischiocerite, merocerite and carpocerite, and 

 articulated with the last an extremely long many-jomtedflagellum 

 or procerite. 



The appendages of the next antecedent somite are the 

 antennules or internal antennae. These consist of three basal 

 joints, the first of which is enlarged and contains the organ of 

 hearing, and of two terminal many-jointed filaments the fiagella 

 which in the Prawn are very short. The first pairjjf cephalic 



