„ „ Note on the structure and relations of the kidney in Aplysia: Mitth. Zool. Stat. Neap. iv. (1883), pp. 420–428. =R. von Erlanger=, On the paired Nephridia of Prosobranchs, etc.: Quart. Journ. Micr. Sc. xxxiii. (1892), pp. 587–623. =H. Fischer=, Recherches sur la Morphologie du Foie des Gastéropodes: Bull. Scient. France Belg. xxiv. (1892), pp. 260–346. =C. Grobben=, Morphologische Studien über den Harn- und Geschlechtsapparat, sowie die Leibeshöhle, der Cephalopoden: Arb. Zool. Inst. Wien, v. (1884), pp. 179–252. „ Die Pericardialdrüse der Gasteropoden: ibid. ix. (1890), pp. 35–56. =B. Haller=, Beiträge zur Kenntniss der Niere der Prosobranchier: Morph. Jahrb. xi. (1885), pp. 1–53. =A. Hancock=, On the structure and homologies of the renal organ in the Nudibranchiate Mollusca: Trans. Linn. Soc. xxiv. (1864), pp. 511–530. =A. Köhler=, Microchemische Untersuchung der Schneckenzungen: Zeits. Gesamm. Naturw. viii. (1856), pp. 106–112. =Ad. Oswald=, Der Rüsselapparat der Prosobranchier: Jena. Zeits. Naturw. N.F. xxi. (1893), pp. 114–162. =R. Perrier=, Recherches sur l’anatomie et l’histologie du rein des Gastéropodes prosobranches: Ann. Sc. Nat. Zool. (7), viii. (1889), pp. 61–315. =C. Semper=, Reisen im Archipelago der Philippinen; Land Pulmonata: Theil ii. Band iii. (1870–77). =C. Troschel=, Das Gebiss der Schnecken: Berlin, 1856–1892. =W. G. Vigelius=, Ueber das Excretionssystem der Cephalopoden: Niederl. Arch. Zool. v. (1880), pp. 115–184. CHAPTER IX THE SHELL, ITS FORM, COMPOSITION AND GROWTH--DESIGNATION OF ITS VARIOUS PARTS The popular names of ‘shells,’ ‘shell-fish,’ and the like, as commonly applied to the Mollusca, the intrinsic beauty and grace of the shells themselves, resulting in the passion for their collection, their durability and ease of preservation, as compared with the non-testaceous portion,--all these considerations tend to unduly exalt the value of the shell as part of the organism as a whole, and to obscure the truth that the shell is by no means the most important of the organs. At the same time it must not be forgotten that the old systems of classification, which were based almost entirely on indications drawn from the shell alone, have been strangely little disturbed by the new principles of arrangement, which depend mainly on structural points in the animal. This fact only tends to emphasise the truth that the shell and animal are in the closest possible connexion, and that the shell is a living part of the organism, and is equally sensitive to external influences.