320 



COMPARATIVE ANATOMY 



CHAP. V. 



thoracic shield. The 5 anterior pairs, which have moved to the neighbourhood of 

 the mouth, have no exopodite in an adult condition, though it is to be found in 

 their larval stages (Fig. 220). They all possess a disc-shaped epipodial appendage 



which serves for respiration. The endo- 

 podite and the protopodite together only 

 contain 5 joints. These 5 anterior pairs 

 of feet are armed with prehensile hooks. 

 Such a prehensile hook is formed by the 

 last joint of a foot moving upon the last 

 joint but one, like the blade of a knife 

 upon its handle. Very powerful hooks 

 of this kind are developed in the 2d pair 

 of limbs for catching prey. The last 3 

 pairs of thoracic feet serve as ambu- 

 latory feet. They are biramose feet with 

 somewhat reduced endopodites ; the 

 exopodite here forms the limb - like 

 prolongation of the protopodite. Epi- 

 podial appendages are wanting. 

 FIG. 220. Thoracic feet of a Squilla larva, In the Schizopoda the thoracic feet 

 after Claus. A, 2d maxillipede. B, one of the a re very interesting, connected on the 

 subsequent 3 thoracic feet, en, Endopodite : ex, -i j , ,v ? j ,1 T * 



exopodite one han( ^ Wltn tllose found in the Lepto- 



straca, and leading on the other to those 



of the Decapoda. All the 8 pairs of thoracic feet are still more or less similarly 

 formed, and are biramose. It is best to describe the Euphausidce first, then the 

 Lophogastridce, and lastly the Mysidce. 



In the Euphausidce (Fig. 221, F-I) the thoracic feet consist of the 2-jointed 

 protopodite, a 5-jointed endopodite, and an exopodite which is composed of a one- 

 jointed shaft and a flagellum which is frequently ringed. All the 8 pairs of thoracic 

 limbs have epipodial appendages on the basal joints of the protopodites ; these 

 appendages are simply pouch-like on the first pair, but are more or less branched on 

 the other pairs, and form gills. The 2 anterior pairs of thoracic feet are slightly 

 different from the subsequent pairs, the proximal joint of the protopodite having 

 a ridge-like process. Herein we see the beginning of the metamorphosis of these 

 thoracic feet into maxillipedes. In Euphausia the endopodite is wanting in the 

 last two pairs, in Thysanopus in the last pair. 



In the Lophogastridce (Fig. 221, A and B] the 1st thoracic foot has already become 

 a maxillipede, and the 2d also approaches the form of one. On the 1st pair the 

 epipodial appendage becomes a broad vibratile plate. In the female brood-lamellse 

 are found on the basal joints of the protopodites of the other feet. Gills arise near 

 this basal joint, but from the integument of the thorax itself; these correspond 

 with the epipodial gills of the Euphausidce, and may be described as appendages 

 dislocated from the proximal joint of the protopodite. 



In the Mysidce (Figs. 201, 221, C-E) both the 2 anterior pairs of thoracic limbs are 

 maxillipedes with masticatory ridges. The first maxillipede carries a vibratile 

 epipodial plate. Some or all the other feet may in the female carry brood-lamellse 

 (Fig. 222). Branchial appendages are wanting on the thoracic limbs of the Mysidce. 

 The Decapoda (Figs. 223, 224, 202, 203) have the three anterior pairs of thoracic 

 feet transformed into maxillipedes, which no longer serve for locomotion but only for 

 taking in food. The exopodite is well developed in them, and flagellate ; the epipod- 

 ite lies in the branchial cavity in the form of a long lamella. In the Brachi- 

 ura it is whip-like and resembles a cleaning foot. The anterior maxillipedes have 



