506 THE VOYAGE OF H.M.S. CHALLENGER. 



outwards towards the eye, then, making a somewhat abruj^t elbow, advance into the lateral 

 parts of the face, ending on a level with, the base of the mandibles. Tlieir ramifications 

 supply the massive muscles of the mouth-organs. The upper aorta at first ascends towards 

 the antennae, then bends forwards and terminates in the upper lip. In its course the aorta 

 forms two vascular rings situated in a vertical median plane, the one round the brain, the 

 next round the cohering bases of the antonnary or " renal " glands. From the lower branch 

 of the pericerebral ring springs a minute single artery ■which supplies the oesophageal nerve- 

 ring. From the upper branch of the pericerebral ring two pairs of lateral branches are given 

 off to the antenna;. Two other pairs originate, one between the pericerebral and perirenal 

 rings, the other beyond the perirenal ring. Finally, a fifth pair of branches forms a 

 pericBSophageal vascular collar, with various ramifications to supply the mouth-organs.] 

 Tlie hinder aorta runs above the intestinal canal to the telson. In Goplana polonica it is furcate 

 at the end, each terminal branch being very short and opening abruptly into the body- 

 cavity. Almost in the middle of the compound segment, the aorta gives off a pair of very 

 short lateral branches, embracing the rectal gland and ending abruptly. The aorta, 

 however, terminatw-differently in other species. 

 The anterior blood-current flowing from the terminal opening of the corresponding aorta moves 

 in the head from before backwards, rises obliquely upwards, enters the thorax just below the 

 stomach, and pursues its course on either side of the intestine and over the liver-tubes. 

 On the way it gives off lateral currents to the mouth-organs and the four first feet with 

 their branchiae, but does not reach beyond the fourth perKOu-segment. From the hinder 

 aorta arise on either side two currents, an anterior from tlie lateral branch (in Goplana 

 piolonica) or the anterior opening (in Gammarus p)uh.t), a posterior from the terminal fork . 

 (in Gammarus polonica) or the terminal opening (in Gammarus pulex). Both currents on 

 either side of the body descend to begin with towards the ventral surface, unite between 

 the articulations of the second and third uropods, and form a common stream which runs 

 forwards on the ventral surface, but at the articulation of the first urojjods with most of its 

 mass ascends, and then flows forwards, divided into two parallel streams. The one stream 

 approaches the intestine just under the hinder aorta, the other, somewhat deeper, approaches 

 the liver-tubes. The ventral stream appears to be of subordinate importance. From the 

 hinder streams lateral currents go to the pleon-appendages and to the four hinder perseopods. 

 Thus the fourth perseon-segment is a boundary which is overstepped neither by the anterior 

 nor the posterior blood-currents, and in it they all unite, and flow on into the second 

 peraBopod. 

 In the pleopods the arterial current descends the front margin, in the uropods the hind margin, 

 while the venous current ascends the opposite side in each set. [Between the four first and 

 the three last feet of the perceon, there is a similar diversity in the direction of the currents. 

 See Delage, 1881, and' Claparfede, 1863; Wrzesniowski gives a reference also to Claparfcde, 

 Etudes sur la circulation chez les aranees du genre Lycosa, 1875.] Into each foot of the 

 pera3on two arterial currents enter, but only a single venous current returns. All these streams 

 pass special openings in the articulation between the side-plate (coxa) and the segment, as 

 .> well as in that between the side-plate and the first joint of the limb (coxa and basis). Each. 



foot possesses a common venous sinus, lying in the under part of the segment above the side- 

 plate, and bounded by the flexors and extensors of the foot. Into this sinus gathers all the 

 blood running back from the foot and its appendages towards the heart. In each branchia 

 the arterial current traverses the hinder rim and passes over by means of numerous tranS'- 

 verse currents into the venous current which pursues its course on the front rim. The venous 

 current of each branchia opens into the common venous sinus of the foot, so that the blood 

 oxidised in the branchia flows direct to the heart, without contributing to the nourishment 

 of the foot. 



