240 



A. IZUKA 



(v. a. c.) and the intestine. In this vessel, contrary to the dorsal, the 

 blood streams in antero-posterior direction ; its wall docs not show 

 peristaltic contraction. 



In most segments of the body, i. e , in all those except the anterior- 

 most few segments and the anal segment, the distribution of branches 

 from the dorsal and the ventral vessel and the connection between 

 these vessels, take place in the following manner. 



The dorsal vessel bears in each segment a symmetrical pair of side 

 blanches, situated one on each side. They may be called the lateral veins 

 (/ :'.). Following it from the point of junction with the dorsal vessel, the 

 lateral vein of either side runs infero-laterally on the inner side of the dorsal 

 longitudinal muscle, turns round the lower ed^re of that muscle outwards 

 and then proceeds supero-laterally towards a point in the upper part of the 

 foot base. Reaching that point, the vein divides at once into the three 

 following veins : i ) the subcutaneous vein (sc. v., figs I and 2) which is 

 directed mediati and runs in the dorsal body-wall along the anterior 

 margin of the segment, taking up on the hind side of its course the 

 subcutaneous capillaries of the parts ; 2) and 3) the superior and inferior 

 parapodial veins which proceed outwards into the upper and the lower 

 ramus respectively of the foot and take up the capillaries of this organ. 

 The blood in the above three vessels passes into the lateral vein, finally 

 to pour itself into the dorsal vessel 



The ventral vessel (v. 7:, fig. 1) sends off likewise a pair of side 

 branches, the lateral arteries (/. a.). These are probably contractile in the 

 basal parts, to judge from the structure of the wall. Each lateral artery 

 takes an obliquely laterally and upwardly directed course over the ventral 

 longitudinal muscle (:■. /. /;/.) towards the parapodial base, where it splits 

 into two branches The lower branch may be called the inferior parapodial 

 artery, (inf. p a.) not of the same segment but of the next posteriorly 

 following segment, since it passes on backwards into the latter and there 

 splits up into capillaries in the lower parapodial ramus. The upper 

 branch continues the course of the lateral artery to a point in the upper 

 part of the parapodial base in the same segment ; there it again divides 



