220 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Interesting in its bearings upon the adaptability of the molluscan 

 organism, is some additional evidence that Litnax agrestis may become 

 carnivorous, and that it may eat dead earthworms and aphides.' Let 

 it be remembered, however, that Hunter kept a sea-gull alive for 

 a year on barley, that rabbits have been known to thrive on frogs, 

 and that cows and horses have been for a considerable period fed 

 on fish.^ 



This brings me to the consideration of the Mollusca in relation 

 to the more advanced work in cytology, now occupying so much 

 attention. 



As the result of appreciation of the extent to which, continuity 

 between the protoplasmic constituents of the animal body may be 

 observed, the extension of ideas opposed to the cell-theory, that 

 were first put upon a broad basis by Heitzmann in 1883,^ in the hands 

 of Sedgwick,* Schuberg," and others, has raised questions of serious 

 modification in our conceptions of the Metazoon. On the other 

 liand, the master minds of Von Kolliker, Eetzius, and Y. Cajal, and 

 their associates, as the result of perfection of improved methods 

 of microchemical technique, have brought about the great generali- 

 zation that that desperate complex, the central nervous and sensory 

 epithelial apparatus, is composed of discontinuous cells and their 

 derivatives, arranged after the manner of a felt and not as a net-work. 



The challenging of the cell-theory, with all recent work on the 

 minute structure of protox)lasm, has concentrated attention on the 

 nucleus ; and of the extreme to which Hertwig, Weismann and their 

 followers have carried their conceptions of the part played by that 

 structure in heredity, I need but remind you. 



In the progress of these vitally interesting lines of inquiry, the 

 Mollusca have come to play no mean part. Tlieir structural units are 

 large ; and so marked are their nuclear elements, that the so-called 

 ' centrosphere ' — the most debatable object among cytologists — may in 

 some of them be readily seen without recourse to reagents. Lymn(na 

 and Siiccinea were among the first animals the nuclei of which arrested 

 the attention of Biitsehli,'^ that pioneer in the study of nuclear division, 

 in the early seventies ; and the term ' amphiaster ' was two years later 

 applied by Fol '' to one of the earliest established phases in the process, 

 after observations upon Pteropoda. In the hands of Mark, Limax 

 campestrin becomes responsible for perhaps the most bulky treatise * 



' C. Oldham, Zoologist, ser. Ill, vol. xx, p. 264; and also F. V. Theobald, t.c, 



p. 307. 

 2 Of. W. II. Flower, Sfvdical Times and Gazette, February, 1S72, p. 217. 

 ^ C. Heitzmann, "Microscopical Morphology of the Animal Body in Health and 



Disease." New York, 1S83. 

 * A. Sedgwick. Cf. Quart. Journ. Micr. Sci. (n.s.), vol. xxxvii, p. 87. 

 5 A. Schuberg, Sitzb. Thy?. Med. Ges. Wiirzb., 1893, p. 44. Ct. also J. A. 



Hanimar, Arch. Mikr. Anat., Bd. xlvii, p. 14. 

 •^ (). Biitschli, Zeitschr. Wiss. Zool., Bd. xxv, p. 201. 

 ■' 11. Fol, Arch Zool. Exper., 1877, p. 147. 

 *^ E. L. Mark, Bull. Mus. Conip. Zool. Harvard, vol vi, p. 173. 



