8 Prof. M'lntosh's Notes from the 



Nowikoff* (1912), illustrated by representations of stained 

 sections, which indicate the position of muscles, nerves, and 

 blood-vessels as well as the skeletogenous elements. He 

 regards the supporting substance as homologous with that 

 in Mollusca and Vertebrates, presenting, moreover, less 

 polygonal or somewhat rounded cells, with ground-substance 

 of a chondro-mucoid character, with nuclei and proto- 

 plasmic contents, and having externally a layer, which he 

 terms perichondrium, upon which the cuticle and its nuclei 

 rest. The author does not go into the distribution of the 

 skeleton in the foregoing forms, but confines his attention 

 chiefly to the histology of the tissue, the so-called " carti- 

 lage "-cells being filled with fluid, and almost resemble 

 plant-cells from their distinctness. They possess one, rarely 

 two, nuclei. The perichondrium is granular and has an 

 alveolar (basement-) layer between it and the hypoderm. 



The structure of the body-wall in Sabella penicil/us, L., 

 is typical, though there are special developments of the 

 surface. Thus, on each side of the mid-ventral line a thick 

 glandular layer outside the circular muscular coat occurs. 

 This appears to be a special development beneath the hypo- 

 derm, which is readily traced over it and along each side of 

 the mid-ventral fissure. The circular muscular coat is well 

 developed and is continuous or nearly so. The dorsal longi- 

 tudinal muscles are in section thick externally, but taper to 

 the mid dorsal line, where a hiatus for the suspensory 

 mesentery of the alimentary canal occurs. These muscles 

 are comparatively narrow and do not reach the lateral edge. 

 In the same way the ventral longitudinal muscles are compact 

 or almond-shaped in section, slightly thinned internally, and 

 each is separated by a wide gap from the muscle of the 

 opposite side. Both dorsal and ventral longitudinal muscles 

 have a translucent sarcolemma on the free surface and both 

 show bands of sarcolemma here and there cutting the mass 

 into various fasciculi. Under the inner edge of each lies 

 the nerve-trunk surrounded by neurilemma and with com- 

 paratively little neuroglia. On the upper and inner edge of 

 each is a large neural canal, which in many sections is larger 

 than the nerve-trunk and is occupied by a coagulable 

 material. It appears to be unnecessary to call such a tube 

 a giant nerve-fibre, and, indeed, the term neural canal was 

 adopted in 1877 f, and may as well comprehend the finer 



* Zeitsch. f. w. Zool. Bel. ciii. p. 68G, Taf. xvi. 



t " On the Arrangement and Relations of the Great Nerve-cords in 

 the Marine Annelids," Proceed. Roy. Soc. Ediu. Session 1870-77. 



