20 Prof. M'Intosh's Notes from the 



than the ventral. The oblique are long and slender, and 

 are fixed over the outer part of the nerve-trunks. 



Passing backward, in the anterior region, the dorsal 

 muscles increase in bulk and pass further downward, the 

 dorsal arch of the body being better developed, and the feet 

 having taken a lateral position somewhat below the middle 

 line. A median hiatus still occurs dorsally, and the muscles 

 increase in thickness from this downward until reaching the 

 blunt cone interiorly. The ventral longitudinal muscles 

 are sausage-shaped in section and now not half the bulk of 

 the dorsal. 



In the middle of the body of Bispira the walls have 

 assumed the normal arrangement, the hypoderm being thin 

 dorsally, thickened laterally, especially on the processes, and 

 considerably diminished (from that in the front) in the 

 mid-ventral line, the ventral area in section being that of a 

 gracefully curved spindle, massive in the middle below the 

 nerves, tapering off at each side, and again having thickened 

 glandular areas in the lateral region with its processes. 

 The dorsal longitudinal muscles are larger, somewhat 

 thinned toward the dorsal middle line, where there is no 

 distinct hiatus at the attachment of the mesentery, and the 

 curve on each side increases in breadth to the lateral 

 processes, where it bends slightly inward, and in some a slight 

 median projection or keel occurs to which the median mesen- 

 tery is attached. These muscles are lined by the coelomic 

 cells with nuclei. The fasciculi in section are fibrillar, and 

 they abut externally on the somewhat thin circular coat 

 and internally on the coelomic surface. The ventral longi- 

 tudinal muscles are less in bulk and more compact, but have 

 similar fasciculi, each having a blunt point in section sloped 

 upward and inward at the nerve-cord, slightly tapered and 

 rounded at the external edge. In the iuterganglionic areas 

 the nerve-cords have the support of the muscle on each side, 

 the inner end often rising above them, and a deep hollow, in 

 which the blood-vessel and its mesentery lie, between them. 

 The neural canals are slightly larger than in front, an 

 additional smaller canal in one case being within the larger 

 on the right, and the investment of each is firm, with a few 

 nuclei, and the usual coagulable contents. They occupy the 

 upper and inner region of each trunk, though a small one 

 occasionally is seen toward the lower border of the cord 

 at the ganglia. The alternation of the slender ventral 

 mesentery with its pigmented cells free in the coelom, and 

 the massive tunnel of crossed fibres with the vessel and its 

 cells inside, and others along the coelomic wall adjoining 



