494 W. R. Coe— Anatomy of Cerebratulus lacteus. 



the cephalic lacunae (Plate X, fig. 1, cl) of which the first lacuna is 

 really the anterior anastomosis. The cephalic lacunae enlarge as they 

 pass backward, one on each side of the rhynchodaeum, from which 

 they are separated only by a very thin- mass of tissue, nearly to the 

 attachment of the proboscis (sect. 98). At this point, thick bands of 

 muscles encroach so much upon their space that the lacunae become 

 very small and thin. Just back of the anterior portion of the brain 

 (sect. 113) the two lacunae enlarge again and become united beneath 

 in a ventral commissure, so that a section here shows a second horse- 

 shoe shaped space (Plate X, fig. 9), but this time with its ends point- 

 ing upward. ^N'ear the side-organs (sects. 123-128) fibres pass from 

 each side obliquely upwards and inwards across the lacuna to the 

 proboscis-sheath, beneath which a portion of the lacuna is separated 

 from the rest to form a median lacuna (fig. 3, ml). A few sec- 

 tions further back this median lacuna communicates with the 

 lateral lacunae, after which it divides into two trunks which supply 

 the mouth and anterior portion of the oesophagus, and to which the 

 name buccal vessels may be given. From the broad ventral anas- 

 tomosis of the cephalic lacunae, and directly above the median lacuna, 

 a small vessel also arises, which becomes surrounded with fibres of the 

 proboscis-sheath and forms the dorsal vessel, described above. Just 

 back of the brain-lobes the lateral lacunae greatly enlarge, and finally 

 completely surround the side-organs, except at their anterior borders, 

 so that these organs project freely into the blood space. In the 

 region of the mouth (Plate X, fig. 4) the lateral lacunae become 

 much smaller and pass backward through the oesophagal region, on 

 each side between the proboscis-sheath and the lateral nerve-cord, as 

 the lateral vessels. These vessels give off to the walls of the 

 oesophagus a multitude of branches (Plate XIII, fig. 1, ov) which 

 break up into minute, anastomosing twigs. In the nephridial region 

 these branches run in close proximity to, and side by side with, the 

 tubules of the nephridial system (fig. 5). Towards the posterior 

 portion of the oesophagal region the lateral vessels are not larger 

 than some of the oesophagal vessels although their appearance varies 

 greatly according to the state of contraction. 



Near the intestinal region the lateral vessels bend downward and 

 occupy a position, for the remainder of their course, beneath the 

 intestinal caeca, somewhat laterally to the median line. Throughout 

 the length of the intestinal region a branch (fig. 1, av) is given off 

 from each lateral vessel beneath every pair of intestinal caeca, to join 

 the dorsal vessel beneath the proboscis-sheath. There is a union of 



