AFFINITIES OF ECIIIUKUS UNICINCTUS. 83 



On comparing the alimeatary canal of allied animals, as described by various authors, 

 Avith this species, I find the part anterior to the intestine has been divided up into 

 numerous distinct regions, llietseli calls it simply " intestin buccal," but Spengel says 

 it comprises a pharynx, oesophagus, and crop. Jameson finds the oesophagus of Echiuras 

 equals the oesophagus and gizzard of Thalassenia. Greefi" does not mention tiie crop, but 

 in other respects his description agrees with that of Spengel. In this Japanese form I 

 can divide the alimentary canal only into those areas mentioned already, i. e. : — 



i. The huccal sac (or pharynx), on the first portion of which arc; the radial mesenteries. 



ii. The coiled part (or crop). 



iii. The narrow straight part (or gizzard). 



iv. The intestine, bearing the ciliated groove and collateral intestine. 



V. The rectum or large intestine, fixed to the left side of the nerve-cord and ending 

 at the anus. 



Figs. 13-18, Plate 8, are diagrammatic representations of transverse sections through 

 these various regions, showing the comparative development of tlie muscular layers and 

 glandular epithelium. 



Blood-Vascular Sijstem. — All the species of the genus Echiarm hitherto investigated 

 possess a very characteristic blood-vascular system. E. Fallasii, according to Greetf, has 

 two main vessels — a dorsal and a ventral — and " beide Gefasse verliinsen sich bis in 

 den Eiissel, das Riickenfass einfach und in der lliickenwandung des Ptiissels des 

 Russelarterie der mittleren Laugsrichtuug folgend das Bauchgefiiss in zwei Aesten, die in 

 den Seitenriiudern uuter Entsendung zalilreicher verlaufeu." In the proboscis he finds 

 an open communication between tlie blood system and the body-cavity ; anteriorly the 

 dorsal vessel swells out as a contractile heart, while the ventral vessel runs to the hinder 

 end of the hody, bound to the ventral surface of the alimentary canal, as the " Darmvene." 



Spengel, in working on the same species, gives a very similar account of its vascular 

 system, though he denies the existence of a communication between the vessels and the 

 body-cavity, and does not give any support to the statement that a pulsatile heart is 

 present dorsally. The vessel which Greelf refers to as the "Darmvene" is, as Spengel 

 shows, the " Nehendarm," or collateral intestine. E. Pallasii, then, according to Spengel 

 and E-ietsch *, has a ventral vessel running the whole length of the body above the nerve- 

 cord, connected anteriorly by a loop with a short vessel on the dorsal surface of the 

 pharynx and oesophagus : these vessels are found in the proboscis. Jameson gives a 

 similar arrangement for Thalassenia neptiini; and Shipley f says : "A closed vascular 

 system exists in Echiurids, consisting of a contractile dorsal vessel running along the 

 dorsal surface of the anterior end of the alimentary canal, and continued along the 

 axis of the proboscis. At the tip of the prohoscis it bifurcates and each branch descends 

 along the edge until it reaches the base, where, having encircled the oesophagus, the 

 two unite, and are continued as the ventral vessel which runs along the dorsal surface 

 of the nerve-cord, and eventually ends blindly. There is also a vessel which passes from 



* M. llietsch : •• Etude sur lea Gephyrieus aimos ou Echiuriens," in Eec. Zool. Suisse, vul. iii. IS8G. 

 t Shipley : Gqjhijrea aud Phoroitls. The Cambridge Xatural History, vol. Li. p. 450. 



