coe: nemerteans of west and northwest coasts. 149 



Thompson (: 02) for the isimilar portions of the ahraentary canal of 

 Zygeupolia. 



The posterior portion of the stomach becomes very much con- 

 stricted because of the great growth of the inner circular muscles of 

 the body walls (PI. 13, fig. 82), but at the posterior end of these 

 muscles it spreads out suddenly into the broad intestinal canal (PI. 14, 

 fig. 88). As shown in PI. 12, fig. 76, there are a few very small in- 

 testinal diverticula anterior to those which are fully developed. The 

 gradation between stomach and intestine is thus apparent, and the 

 demarcation is as gradual histologically as anatomically, as in 

 Zygeupolia. The intestinal diverticula are very deep (PI. 12, 

 fig. 76 ; PI. 14, fig. 87) and are often forked distally, very much as 

 in Cerebratulus. 



Blood vascular system. — In the portions of the head in front of 

 the brain we find Yevy large blood lacunae, which are much inter- 

 rupted and divided into communicatiijg chambers by fibrous strands 

 of tissue extending from the dorsal to the ventral sides (PI. 12, fig. 

 78). The lacunae of the two sides find aV)undant channels of com- 

 munication through lacunae lying both above and below the rhyn- 

 chodaeum. The anterior ends of some of these lacunae are lined 

 with clusters of deeply staining gland cells, the secretions of which 

 are discharged directly into the blood s])aces. They resemble the 

 clusters of glands found in certain portions of the rhynchocoel in 

 various other species. 



At the anterior end of the mouth, and immediately behind the 

 attachment of the proboscis to the rhynchodaeum, the lateral blood 

 spaces become divided into a dorsal and a ventral pair of vessels, as 

 in the other species of the genus. The ventral pair constitute the 

 main lateral vessels which extend throughout the length of the 

 body, while the dorsal pair unite with the ventral just back of the 

 nephridial region. The ventral are distinguished from the dorsal 

 not only by position, but also in having much thicker walls — that 

 is to say, the ventral vessels have a strong fibrous sheath, while the 

 dorsal are mere spaces in the parenchyma with extremely few fibers 

 in their Avails. It often happens that the ventral appear much 

 smaller than the dorsal vessels, but this is probably because the con- 

 tractile fibers of the former contract so as to greatly diminish the 

 size of the vessel on the death of the animal, just as the arteries, 

 with their more muscular walls, are smaller than the corresponding 

 veins in the dead body of a vertebrate. 



