232 



Messrs. J. E. S. Moore and W. B. Eandles. [Mar. 17, 



They have long been known to exist in these orders, but have never 

 been adequately dealt with from a morphological point of view. Both 

 have hitherto been regarded as enigmatical structures, capricious in 

 their appearance or non-appearance, and in their relationships. 



The first of these organs, the so-called crystalline style-sac, which 

 characterises the stomach of some Lamellibranchiata, was shown by 

 Collier' 55 ' in 1829 to be present also in several Gastropods. These 

 results were subsequently confirmed by Huxleyf in the case of Ptero- 

 ceras, and they have much more recently been both confirmed and 

 extended by Martin Woodward! and one of us.§ 



From these observations, there seems to be little room left for doubt, 

 that when present, the style-sacs both of the Lamellibranehs and the 

 Gastropods are homologous, and their appearance in two such widely 

 separated groups indicates that they are of considerable antiquity. 

 Or in other words, the species which possess these organs are primitive 

 in that respect. The same may be said of the spiral caecum, for it 

 occurs as an appendage of the stomach in many forms of rhipidoglossate 

 Gastropods, and it is also found in relation to the gastric tubes of the 

 Cephalopods. Until lately the spiral caecum had not been observed in 

 any but the most primitive of rhipidoglossate Gastropods, such as 

 Pleurotomaria and Haliotis, but it is present in those forms of Khipido- 

 glossa where one gill has become suppressed, such as Trochus, and quite 

 recently it has been shown by one of us|| that both the spiral caecum 

 and the style-sac occur together as appendages to the stomach of the 

 prosobranch Nassopsis. Still more recently this same association of 

 style-sac and caecum in the gastric apparatus of the Prosobranchiata has 

 been found to exist in the genera Limnotrochus and Chytra,1I both of 



* " General Observations upon Univalves," printed in the ' Edinburgh New 

 Philosophical Journal ' for 1829, p. 231. 



f Speaking with wonderful acumen, when we think of the date — 1853 — Huxley 

 says : — " Of the pyloric sac — this appears in various forms in a great number of 

 the Mollusca, and seems to be always in a special relation with the liver. In 

 Atlanta it has been seen that its glandular parietes form the liver. In the Cephalo- 

 poda, the hepatic ducts enter its representative, the spiral sac of Octopoda, the 

 elongated sac of Loligo. 



'•' In Pteroceras a very remarkable structure exists, which, so far as I am aware, 

 has not yet been noticed. The existence of a crystalline style in connection with 

 the alimentary canal, has long been known in the Lamellibranchiata, but it has 

 hitherto been supposed to be confined to them. However, in Pteroceras, the 

 pyloric sac contains a very complete style." T. H. Huxley " On the Morphology 

 of the Cephalous Mollusca," ' Phil. Trans.,' vol. 143, 1853, p. 60. 



t ' Proc. Mai. Soc.,' vol. 1, p. 143, 1893—1895. 



§ J. E. S. Moore, " The Molluscs of the Great African Lakes," ' Quart. Journ. 

 Microsc. Sci.,' vol. 41, p. 199, 200. 



|| J. E. S. Moore, " The Molluscs of the Great African Lakes, Nassopsis and 

 Bythoceras," ' Quart. Journ. Microsc. Sci.,' vol. 42, p. 190. 



% Miss Digby, 'Journ. Linn. Soc, Zool.,' vol. 28, p. 434. 



