THE MOLLUSOAN RADULA. 



123 



witli borax carmine. Bethe's stain acts readily on those 

 parts which resist borax carmine and remain unstained in 

 ribbons treated with borax carmine only,^ 



The action of hydrofluoric acid renders it possible to make 

 sections of the radula ; these reveal the organic matter as a 

 solid basis having the form of the complete structures. With 

 the ordinary stains the cusps are less deeply coloured than the 

 roots of the lateral teeth (text-fig. 1), with Bethe's stain the 

 bases of the roots of these teeth and parts of the marginals 



Text-Figuue 1. — A longitudinal section of the radula of Patella 

 vulgata after treatment with strong hydrofluoric acid and staining 

 with iron lisematoxylin. t. s. m. Tensor superior muscle, b. e. Basal 

 epithelium, c. Organic basis of the cusps, r. e. Roofing epithelium. 



1 Bethe's method: the object is placed in a 10 per cent, aqueous solution 

 of anilin hydrochloride to which one drop of fuming hydrochloric acid is 

 added for every 10 c.c. of water. After washing thoroughly the object is 

 transferred to a 10 per cent, solution of potassium bichromate. It will be seen 

 that at the young end of the Patella ribbon each row of teeth is uniformly 

 coloured by the carmine stain, the youngest teeth are paler than those imme- 

 diately in front of them. In front, again, of the darker red teeth the roots 

 of the laterals and centrals (inner laterals) are coloured green by Bethe's 

 stain, their cusps being still red like the marginals. Pinally, as we pass 

 forwards, the cusps become golden-yellow and then red-brown owing to the 

 presence of iron oxide, and tiie innermost marginal bears a band of green. 

 The contrast in staining properties between the marginals and remaining teeth 

 is very striking. The basal membrane itself is red, but in the preparation it 

 has been removed as far as possible, as it obscures the differentiation in 

 specimens mounted whole. These differences in staining properties are to be 

 found with greater or less deviations in the radula of other odontophorous 

 molluscs. 



