51 



often appears to be continuous round two or more cells 

 (fig. 23). The more cells round which it is continued the 

 thicker it is, and hence in places there appear to be septa 

 running into the mass and forming at the same time the 

 bounding walls of contiguous cells. The cartilage of the 

 molluscan odontophore has often been referred to by 

 writers, but has apparently never been examined in any 

 detail. It has been compared to cellular or vesicular 

 connective tissue, or called cartilage without micro- 

 chemical tests. Josef Schaffer seems to be the only 

 worker who has examined it in any detail, but his paper 

 has appeared only as a resume without illustrations. 

 The main conclusion is that the " cartilages " vary 

 towards or away from a distinctly real cartilage, and that 

 the development of a low or high type of cartilage is to a 

 certain extent independent of the phyletic position of the 

 animal. The Buccinum cartilage is most certainly a real 

 cartilage. Micro-chemically it reacts in a slight but 

 distinct manner to thionin, giving the characteristic 

 muco stain. It is therefore to a certain extent a muco- 

 cartilage. 



The odontophoral cartilage is not entirely composed 

 of cartilage tissue, as the dorsal portions of the walls of 

 the groove (fig. 23, Ling, con.) are of a very compact con- 

 nective tissue, composed of a matrix resembling the inter- 

 cellular matrix of the cartilage area, but penetrated by 

 a large number of muscle fibres. 



The muscle fibres (fig. 22) of the radula are also 

 striking in structure. They are red in colour, and 

 contain much sarcoplasm. Each muscle cell is a spindle- 

 shaped structure of considerable length. In section it is 

 circular, and the diameter of these fibres is considerable, 

 15//. The sarcostyles (fig. 22, Mus. col.), or actual 

 contractile elements, are arranged round the periphery of 



