356 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



states, that though fixed in front the vessels are elsewhere free, and only con- 

 nected here and there to the body- wall by ligamentous bridles; and in one of his 

 plates* figures the ova between the lateral vessels and the wall of the body. 

 All our transverse sections show that such could hardly occur, for the vessels 

 occupy a secure position beneath the nerve-trunks; and while the ovaries or 

 sperm-sacs sometimes press the vessels downwards towards the ventral surface, 

 and increase the distance between them and the nerve-trunks, they never actually 

 intervene between the latter and the body- wall in the perfect worm. 



Many of the older authors confounded the ganglia with hearts, such as 

 Eheenberg, Huschke, Delle Chiaje, Duges, CErsted, and more recently our 

 countrymen, Drs Williams and Johnston, The latter mentions that the only 

 blood-vessel he has seen is one " winding down the middle, along the surface of 

 the alimentary canal," but he can neither trace its origin nor termination. I)r 

 Max Schultze| seems to have mistaken the edge of the proboscidian sheath 

 under pressure for the blood-system, which he figures as two long straight trunks 

 on each side of the digestive tract. The true blood-vessels he describes as the 

 water-vascular system, but shows neither beginning nor ending, though numerous 

 large branches are represented as issuing from them throughout their course. 

 Prof. Keferstein^: does not distinguish with sufficient clearness the different blood- 

 systems of the Ommatopleans and the Borlasians; and, indeed, applies the 

 definition of the former to the latter ; but so far as they go his descriptions and 

 representations of the arrangement in this group are good. He, moreover, shows 

 an elaborate series of minute transverse anastomosing vessels in his Borlasia 

 splendida, whose structure therefore differs from that usually exhibited by the 

 British Ommatopleans. M. Claparede,§ though his publication is more recent, is 

 less correct than the latter author, for he figures the dorsal vessel as passing above 

 the ganglionic commissure before giving off the anastomotic to join the lateral, 

 and thus a somewhat stiff square is formed in the cephalic region, while the lateral 

 vessels have to pass to the outside and front of the ganglia before meeting the 

 anastomotic. The vessel appears also to be placed on the dorsum of the proboscis. 



Nervous System. —In the living animal two carmine, pinkish, or reddish color- 

 ations are observed on the snout some distance behind the tip : these mark the 

 position of the cephalic ganglia or nervous centres. As previously mentioned not 

 a few authors, misled by their colour, pronounced them to be hearts. The aspect 

 of the ganglia under pressure is indicated in Plate VI. figs. 1 and 3, h ; and in 

 large specimens they are pear-shaped under a lens. Each ganglion consists of 

 two divisions— a superior, shaped somewhat like an almond, and an inferior, 

 continuous with the great nerve-trunks. The first-mentioned portion is chiefly 



* Op. cit. pi. xxi. fig. 3. Polia sanguirubra. f Op. cit. p. 64, pi. vi. fig. 2. 



} Zeitsch. fur wiss. Zool. pp. 85-87, taf. v. & vi.j § Beobach. iiber. &c, taf. v. fig. 10. 



