302 TRAXSACTIOXS LIVERPOOL BIOLOGICAL SOCIETY. 



Lateral -4. 4. 4. 4. 4. 3&4. 3 & 4. 4&5. 

 Central - 5. 6. 7. 6-8. 9. 6. 7. 8. 



Cases - 8. 12. 2. 1. 1. 1. 1. 1. 



It will be seen that even the bilateral symmetry may 

 be destroyed, the opposite lateral teeth having a different 

 number of denticles. Furthermore, though in almost 

 all cases the teeth are the same on the one radula, there 

 have been observed specimens where the number of 

 denticles on the anterior central teeth was less than the 

 number at the posterior end of the radula. 



Histology of Odon top h oral Cartilage 

 a n d E a d u 1 a i- Muscle s. 



The cartilage of the moUuscan radula (fig. 23) 

 represents probably the earliest development of cartilage 

 in the animal kingdom, and by reason of its distinctness 

 and ease of preparation it is a good example for the study 

 of invertebrate cartilage. 



The most external bounding layer is a delicate 

 connective tissue, which encloses the cartilage cells. The 

 cartilage itself has the appearance of a plant tissue. It 

 seems at first sight to be composed of very large irregular 

 cells with small round nuclei and extremely definite and 

 deeply staining cell walls. The cells (fig. 22, Cart.) are 

 18/i in diameter, turgid with fluid, and contain a 

 delicate fibrillar protoplasm which does not stain 

 intensely owing to its attenuated state. The nuclei 

 (fig. 22, Nuc), which are perfectly spherical, are only 

 4/x in diameter. A nucleolus is usually present and 

 many small granules of chromatin. The apparent cell 

 walls are in reality tlie intercellular matrix formed by 

 the cells. This is small in quantity and is formed in such 

 a regular manner that it has the appearance of cell walls 

 rather than a matrix. This pseudo-wall, if followed, 



