SCIENCE-GOSSIP. 



THE ODONTOPHORES OF MOLLUSCA. 

 By E. W. Wake Bowell. 



T N these days, when the microscope has become 

 part of the necessary outfit of the naturalist, it 

 is somewhat remarkable how little attention is 

 given to the odontophores of our native Mollusca. 

 Most of the current manuals of British shell-lore 

 inform us that "these beautiful objects" may be 

 extracted by means of a spirit-lamp, test-tube and 

 caustic potash. Statistics have also been published 

 in such books explaining that certain species have 

 so many rows of so many teeth each, totalling up 

 to so many thousand teeth. Learned professors 

 have concocted Greek names for various forms of 

 odontophore only less remarkable than the objects 

 themselves. It seems to be generally understood 

 that odontophores are worthy of study ; and yet 

 how seldom do we come across anybody who knows 

 anything about them. We are told that it is a 

 question of "internal anatomy"; but if it be 

 so, the difficulties attending the study are not 

 prohibitive, and it might well be taken up by 

 naturalists, who would pause' before dogmatising 

 concerning the intestinal convolutions of a slug. 

 It is in the hope of interesting some of the less 

 advanced students of malacology that the following 

 notes are written. 



The majority of workers at this subject, so far 

 as I can gather, do not stain their preparations ; 

 and they mount, not in balsam, but in glycerine jelly. 

 I think there are good reasons for departing from 

 their practice. An unstained preparation may be 

 intelligible in the case of the larger species, but 

 when we come to such forms as Conuhis or the 

 Vertigines, very little can be made out, even if the 

 form of the " teeth " is previously known to the 

 investigator. I find that all species are very much 

 better for a stain. One cannot expect to get a 

 sharp definition of the teeth (by staining) at the 

 middle and front of the odontophore, but one can 

 often get preparations showing with wonderful 

 distinctness the recently-formed ones at the 

 extreme back of the organ. It is just these teeth 

 which are worth studying. Those which are in 

 actual use generally get rubbed down very soon, 

 and show a blunt apex ; such have frequently been 

 figured as the normal form of the tooth. It is 

 practically convenient that these last-formed teeth 

 should be the subject of our quest, since that part 

 of the membrane is much more easily extended to 

 advantage on the slide. 



My process is briefly as follows : (i) in the 

 case of the larger species the radula sac, with its 

 muscles, is dissected out — generally a very easy 

 operation. The smaller snails are, if possible, 

 separated from their shells. The portion of the 



animal thus obtained is boiled up with a few drops 

 of liquor potasse in a watch-glass. Some care is 

 needed in this operation, and it is well to do it as 

 slowly as possible. A test-tube is hardly to be 

 recommended, because of the great probability of 

 violent projection of potash and contents ; also it 

 is exceedingly difficult to find a small radula in a 

 test-tube. The softer parts will be destroyed by 

 the caustic alkali, leaving the desired radula and 

 the "jaws" or maxilla. (2) These are fished out 

 of the watch-glass and washed in water, the vessel 

 in which this is done being dependent on the size 

 of the objects. Next the radula is separated from 

 the maxilla, which may be dehydrated and cleared 

 for a second preparation. (3) I then stain on a 

 clean slide with Ehrlich's hematoxylin, not dilute. 

 The time taken in staining varies from three to ten 

 minutes, according to the character of the radula ; 

 but any over-staining can easily be corrected by a 

 momentary sojourn in alcohol (or water) just 

 faintly acidulated with hydrochloric acid. This 

 must, however, be done after the blue colour of 

 the hematoxylin has been brought out by washing 

 in tap-water. One can then see whether the blue 

 stain is too deep. (4) It may be that the points of 

 the teeth, as well as the outlines of the basal- 

 plates, are clearly enough indicated in the 

 specimen as it stands ; but this is not generally 

 the case, so we add a second stain which 

 will bring out these important details. The very 

 best medium that I have come across is a satu- 

 rated aqueous solution of ordinary eosin (*). I 

 have tried a great many other coal-tar colours, 

 but none is as good as the eosin, which, moreover, 

 stains very quickly (five to ten minutes), and is not 

 removed in toto by subsequent operations. I may 

 as well add that all preparations of carmine that I 

 have tried are absolutely useless for the purpose ( 2 ) . 

 The hematoxylin staining is not in all cases 

 essential, but it generally very greatly improves 

 the effect even when it does not stain the points of 

 the teeth. It has a way of slightly staining the 

 edges of structures which renders it very useful, 

 especially when followed by eosin, which, so to 

 speak, does the filling up. A Testacella radula very 

 slightly stained with hematoxylin is a great 

 advance on an unstained one, though there is no 

 difficulty in this case in seeing the teeth with the 

 naked eye. (5) The next process is dehydration 

 with alcohol, followed by clearing with oil of ceda 



(') Mine was obtained, through a chemist, iron) Messrs. 

 Hearon, Squire and Francis. The hzematoxylin is best 

 from GrLibler. 



( 2 ) Mr. A. E. Boycott states that one sometimes gets interest- 

 ing and curious results with picro-carmine. 



