MOUTH-PARTS OF THE PALJEMONID PRAWNS. 61 



not developed between the first and second or between the third 

 and fourth segments — as, for instance, in Anisocaris (text-fig. 17), 

 which is an instructive case of this condition. The first endite is 

 frequently absent, whether or not its segment be present as a 

 separate entity. In the Peracarida, the number of endites is 

 generally reduced in this way to three (or fewer, if another of 

 them be absent), though the Mysidacea at first appear to form an 

 exception. In Mysis, however, closer examination reveals a con- 

 dition which may be described as follows. The edge of the second 

 segment proximal to its endite is rounded, meets the base of the 

 endite in a notch, and bears a row of bristles which is continued 

 from the notch across the origin of the endite. The notch forms 

 an outline which simulates the cleft lobe formed in Eucarida by 

 the first two endites. If this suggestion be correct, the Mysi- 

 dacea, Hike other Peracarida, must be regarded as having lost the 

 first endite of the maxilla. In Leptostraca (text-fig. 14), Anaspi- 

 dacea, Stomatopoda (text-fig. 19), and typical members of the 

 Eucarida (text-figs. 15-17), it is present. The degree to which 

 the first and second, and again the second and third, endites are 

 associated to form cleft lobes varies, and is highest in some 

 Decapoda. I shall allude to these double structures — the so- 

 called " lacinire " of the maxilla — as the first and second lobes. 

 The first comprises the endites of the precoxa and coxopodite, 

 the second those of the basipodite. The fifth endite is often 

 represented in the adult by a slight swelling at the base of the 

 endopodite. The exopodite (scaphognathite) is a little-modified 

 fiabellum, and a small rounded lobe proximal to it in Eucarida 

 perhaps represents the epipodite. 



In the first maxilliped of Decapoda (text-fig. 48) the third 

 and second endites are distinct. The latter is often marked 

 by a slight notch, which, however, is not likely to indicate the 

 presence of the first endite, the precoxa being probably fused 

 with the body in the thoracic segments of this group. In 

 Anaspides, as is shown by the history of the development of the 

 gill-rudiments (text-fig. 12), the first and second endites are both 

 present, and the basal joint carries also two epipodites, from 

 which it would appear that the precoxa in this genus is fused 

 with the coxopodite. The Peracarida probably agree with 

 Anaspides in this respect, as they have two epipodites (oostegite 

 and gill) upon the basal joints of the thoracic limbs. Endites 

 may be present upon the endopodite of the maxilliped in the 

 Peracarida, as in Mysis (and perhaps also in Gammarus, but in 

 the latter there is some doubt about the identity of the apparent 

 ischiopodite which bears the endite in question : see footnote to 

 p. 53). Knobs bearing bristles which sometimes appear upon 

 the coxopodites of the second and third maxilliped of prawns 

 (text-figs. 49, 50) may represent the second endite, and a similar 

 knob in the sternal region at the base of the second maxilliped 

 may be a vestige of the gnathobase. 



