4S Prof. M'Iutosli*s Xotes frotn the 



and may he |)resont oi' absent, as iu FHo^rcDia, with por- 

 lilt'xins; ituliffirence, whilst iu other forms tlicir stability 

 ami characteristic! shape have made them of s])ecific im- 

 portance. It is interesting; in connection with the 

 branchial view of the ()])ercnlHr stalk that transverse bars 

 of bluish j)i<j;mcnt are occasionally seen on it. 



Miiscu/ar Sys/cni. — luinudiatcly behind the brain muscular 

 bands })afes from the sides of the ventral to the dorsal wall 

 (or vice versd), some of tlie same side being attached to the 

 base of the opercular stalk dorsally — indeed, they seem to be 

 strongest and best develo[)cdat first on that side. Ventrally 

 they are inserted on each side of the nerve-cord, and 

 by-and-by they bound the thoracic glandular organ on its 

 inner border. 



Behind the ganglia and the opercular stalk the body-wall 

 assumes a more symmetrical outline, and tlie dorsal longi- 

 tudinal muscles become more di^tinct and quite separate 

 from each other, but the ventral longitudinal muscles are 

 indistinguishable. In the median ventral region, however, a 

 special thin longitudinal muscular band oceui's ou each side, 

 and continues backward a short distance — disappearing as 

 the actual ventral longitudinal muscles become distinct. 

 These ventral longitudinal muscles are formed by fibres on 

 the lateral region of the body-wall outside the anterior 

 glandular organ and its appendix, and not in contact with 

 the nerve-cords, which ai'e separated from them by a (,'on- 

 siderable interval. Their outline in transverse section is 

 elliptical, and, as the glandular organ in its [)rogress back- 

 ward diminishes, the fii)res seem to pass externally ; then, as 

 the glandular tube disappears they form a thin stratum to 

 the outer side of the nerve-trunks and in contact with 

 them, the anterior median ventral fibres being still visible 

 between the nerve-trunks. By-and-by the median, or pseudo- 

 ventral, or an.terior ventral, fibres (PI. V. fig. 26, 7w.-) dis- 

 appear from the middle line, and the ventral longitudinal 

 form a spindle-shaped layer in section, separated by an 

 interval from the dorsal, which bend inward at their lower 

 ends, whereas the ventral pass outward below and beyond 

 them. The dorsal and the ventral longitndinal muscles, 

 however, by-and-l)y fall into line and the body-wall becomes 

 more compact, the dorsal muscles retaining the great 

 preponderance in bulk, and closely approximated to the 

 ventral, only a slight incurvation of the inner surface and 

 traces of the oblique muscle indicating the line of separation ; 

 yet the distinctly pennate arrarigement of the fasciculi 

 of the dorsal is characteristic. The nerve-cords are more 



