W. R. Coe — Anatomy of Cerehratulus lacteus. 493 



between the intestine proper and the anus. The rectum is clothed 

 with a single layer of columnar, ciliated epithelium. The anus is at 

 the end of the body, just beneath the caudal papilla. 



The Blood- vascular System. 



The blood is contained in vessels with muscular walls and in thin- 

 walled lacunae. It consists of a colorless plasma in which float 

 spherical corpuscles (Plate XIII, flg. 11) about .006™™ in diameter, 

 each with a spherical, deep-staining nucleus. As in all Schizonemer- 

 teans the blood system (Plate XIII, fig. 1) consists chiefly of three 

 longitudinal trunks reaching the whole length of the animal, and 

 connected anteriorly by means of lacunae and posteriorly by numer- 

 ous transverse, anastomosing branches. Of these three main trunks, 

 two are paired, being known as the lateral vessels {Iv), and arise, 

 one on each side, as posterior continuations of the lateral cephalic 

 lacunae [cl). They j)ass backwards through the oesophagal region on 

 either side of the proboscis-sheath and above the oesophagus, to the 

 walls of which they give off numerous branches ^(ow). In the intes- 

 tinal region they assume a ventral and lateral position beneath the 

 intestine. The third, or dorsal^ vessel (db) arises from the ventral 

 commissure of the cephalic lacunae, described below, passes through 

 the walls of the proboscis-sheath, and continues between the muscles 

 of the same and its internal endothelium (Plate XI, fig. 3) to 

 the intestinal region. Here it again passes obliquely through the 

 proboscis-sheath, directly beneath which (fig. 4) it continues to the 

 end of the body, giving off on the way a pair of branches, which 

 anastomose with the lateral trunks, opposite each pair of intestinal 

 caeca.* 



A description in detail of this system of vessels, taken from a 

 series of transverse sections, each .025™'" thick, may prove of inter- 

 est. Near the tip of the head (section 18 in one series) there is 

 observed a small, thin-walled lacuna lying just above the proboscis- 

 opening. This lacuna spreads out and bends downward on each side 

 of the rhynchodaeum, so that a section of the lacuna in this region is 

 horse-shoe shaped. A few sections farther back this lacuna divides 

 into two portions, crescent-shaped in transverse section. These are 



* Joubin (11), in describing the anatomy of Neraerteans in general, figures these 

 anastomosing vessels between tlie intestinal casca and states, on p. 21, that such is 

 their position. In all those species which I have examined, on the contrary, these 

 vessels do not alternate with the intestinal c?eca but lie opposite them. Cf. Plate XIV, 

 figs. 8, 10, 11. 



Trans. Conn, Acad., Vol. IX. June, 1895 



34 



