362 



COMPARATIVE ANATOMY 



CHAP. V 



It follows, from the above description, that in the Amphipoda the arterial blood 

 cannot in any way be sharply distinguished from the venous blood. 



Anisopoda. This division of the 

 Arthrostraca, though in many points 

 approaching more nearly the organ- 

 isation of the Isopoda than that of 

 the Amphipoda, shows in its blood- 

 vascular system greater similarity to 

 the latter. Two abdominal aortae, 

 however, arise from the posterior end 

 of the thoracic heart, and the peri- 

 cardial sinus is continued into the 

 abdomen. The heart of Apseudes 

 possesses two. ostia on the left side 

 and only one on the right ; in youth 

 the 2 pairs of ostia are present. As 

 to the significance of this fact see 

 below (p. 367). 



In all Arthrostraca the paired 

 ostia, as well as the points of origin 

 of the aorta are provided with valves. 



Thoraeostraea, The cir- 

 culatory system here is linked 

 on to that of the Isopoda. Start- 

 ing with the Stomatopoda, the 

 circulatory system of the older 

 larvae of SquUla, known as 

 A lima and Erichthus, which can 

 hardly be distinguished from 

 that of the adult, have been 

 the most carefully investigated. 

 The heart (Fig. 243) extends 

 as a many -chambered dorsal 

 vessel from the maxillar region 

 (behind the stomach) through 



the thorax and the abdomen to 

 f i 1p pTir i n f f i 1p K^ -hr]'! 

 tllG end Ot 6 5 abdominal 

 Segment. 1WO divisions Can 



b e distinguished in it, a short, 

 l nrio . Tin< , 

 lon g P os ' 



terior division. Probably the 



anterior division alone cor- 



FIG. 242. Diagram of the circulatory system of 

 theAmphipoda,fn>mtheside(afterDelage). Mostof 

 the lettering as in Fig. 240. pt, Pericardial vessels 

 rising from the epimeres (ep), extremities (brf), and 



gills (br) of the thorax ; pa, pericardial vessels of the ... anfpr : or flTir ] 

 abdomen ; s, ventral sinus ; ep, epimeres. The epi- W1Cle anterior > ancl 

 meres of the thoracic segments IV and V partly cut 



off ; pi, pieopoda. 



FIG. 243. Circulatory system of an older Squilla larva before it has passed into the SquUla 

 form (after Glaus), h, Heart, continued posteriorly into the many - chambered dorsal vessel 

 which is richly provided with pairs of ostia (o) ; ac, cephalic aorta ; ao, optic artery ; adi, oao, 

 arteries of the two pairs of antennae ; am, marginal artery of the dorsal shell ; ast, arteria sternalis ; 

 al, hepatic artery ; as, shell artery ; en, 1st lateral artery of the dorsal vessel ; aabi to o6 6 , lateral 

 arteries of the abdomen ; dr, glandular saccules on the hind-gut ; I, hepatic lobes in the telson ; 

 p fi , 6th pleopod (uropod) ; Tcb, branchial leaves (epipodial appendages of the oral feet). 



