38 ART. 8. 1. IKEDA : THREE NEW AND 



inserts itself on the ventral body-wall on the right of the nerve- 

 cord. 



The heart and the ventral vessel are joined by a relatively 

 short (8-4 cm.) commissnre or neuro-intestinal vessel (fig. 23, n:i). 

 This arises from the heart with two roots, so that it presents 

 the shape of an inverted Y. The ventral vessel (figs. 18, 20, 23 

 and 29, v.v.) runs throughout its length just above and along 

 the ventral nerve-cord. Like this it bifurcates immediately be- 

 hind the mouth. The two vessels thus formed 2>roceed into the 

 proboscis and constitute the lateral vessels of that organ (fig. 20, 

 I.V.). In three specimens out of the six dissected, I have ascer- 

 tained the presence, on the ventral vessel, of a peculiar slender 

 branch which probably corresponds to the ring-vessel described 

 by Spengel ('8o) from Echiurus pallaslL The vessel in question 

 (figs. 19 and 20, r.v.) branches off' from the ventral vessel at a 

 point about 1 cm. behind the ventral hooks and runs forwards 

 over and beyond the interbasal muscle of the hooks. Arrived 

 at a close proximity to the bifurcation point of the ventral 

 vessel (see fig. 20), the vessel under treatment {r.m.) splits into 

 three short branches. Of these the two lateral branches soon 

 join the roots of the lateral vessels [Lv.) of the same side, while 

 the single median branch connnunicates with the anterior end 

 of the ventral vessel at the bifurcation point. 



As regards the finer structure of the heart and the ■ vessels, 

 1 have scarcely anything to add to what is already known from 

 other Echiuroids. Only let it be mentioned that the ventral vessel 

 of the ventral vessel has an internal lining epithelium consisting 

 of tall club-shaped cells with the swollen rounded end projecting 

 more or less free into the lumen. Sec ept. in fig. 42, which 

 shows a longitudinal section of the wall of the vessel in question. 



