448 Prof. W. J. Sollas on the 



stain them blue after treatment with sulphuric acid (v.) : a 

 5-per-cent. sohition of potash hydrate dissolves them ; but the 

 resulting solution does not reduce copper from Fehling's solu- 

 tion (vi.). By (i.) they are proved not to be any common 

 form of starch, by (ii.) not fat, by (iii.) not inulin, by (iv.) not 

 tunicin, by (v.) not cellulose, and by (vi.) not sugar. What 

 they are, not one test indicates ; and one is led to think they 

 may be some kind of albuminoid. 



Another constituent of the mesoderm is furnished by the 

 muscle-fibres, which occur chiefly as forming the sphincters 

 about the openings of the vesicles (PI. XVII. tig. 47). They 

 are fusiform bodies prolonged at each end into long slender 

 filaments, 0*0002 inch across where broadest, and 0*014 inch in 

 length, composed of granular protoplasm, which stains deeply 

 witii carmine, and is thus rendered very distinct amidst the 

 unstained colourless jelly of the matrix, and containing in the 

 middle a round, or more usually oval, nucleus 0*000148 inch 

 broad, with fluid contents and a minute round nucleolus. 

 Occasionally the body of the fibre exhibits very distinct 

 longitudinal striation. The muscle-fibres lie side by side 

 concentrically arranged, to form the sphincters ; the ends of 

 some of those towards the outside of the sphincters escape 

 from them tangentially, and wander into the surrounding 

 matrix, where they appear to become connected wath the fine 

 terminations of the connective-tissue corpuscles — a union still 

 further suggestive for the latter bodies of a nervous function. 



Fibres similar, but differing in slight details from those of 

 the sphincter, run radiately from its outer margin into the 

 surrounding tissue ; these are connective-tissue corpuscles. 



Large amoebiform cells with pseudopodium-like processes, 

 gigantic oval nuclei, and included spherical nucleoli are to be 

 seen here and there in the mesoderm (PI. XVII. tig. 48). 

 They never occur in definite Jacunfe, like the similar cells of 

 Tetilla. It is probable that they become converted into 

 sperm-balls, like those to be presently mentioned. 



Spicule-cells have been already mentioned in connexion 

 with the spinispirules ; these little spicules are frequently found 

 with an accumulation of protoplasm about their shafts, which 

 extends as a granular fibre over their spines, and contains a 

 small round nucleus with a nucleolus. The large quadri- 

 radiate spinispirules occasionally, but not often, present cases 

 of indubitably associated nuclei. The large body-spicules 

 frequently bear on one side of the shaft a large cell, something 

 like the amoebiform cells noticed above, the granular proto- 

 plasm of which extends into a thin film, traceable for greater 

 or less distances along the spicule, just as described in similar 



