Ii6 DESCRIPTIONS OF PREPARATIONS. 



The chromogen, called myohaematin by MacMunn, is found in the buccal 

 muscles (and in the heart) of Helix, Arion, Limax and of other Pulmonata. 

 According to Ray Lankester, haemoglobin occurs in the buccal mass of some 

 Mollusca. 



The form and number of the teeth in a transverse row are very variable in 

 the Glossophora. In Pulmonata a median tooth may be distinguished from an 

 indefinite number of admedian teeth. Such a dentition may be formulated thus 

 oo . i . oo , and is termed myrioglossate. Various technical terms have been applied 

 to the variations in number and arrangement of the teeth already alluded to. A 

 median tooth may be present or absent : so too admedian teeth : and in the 

 arrangement known as rhipidoglossate lateral may be distinguished from admedian 

 and median teeth. The size and shape of the teeth themselves are also extremely 

 variable. In the Pulmonata each tooth is provided with a recurved hook, usually 

 simple, but sometimes denticulated \ 



The more or less chitinoid jaw lies on the dorsal aspect of the oral cavity. 

 In most Helices it is a crescentic plate ; its free surface provided with antero-pos- 

 terior ridges. The form of the jaw varies in different Pulmonata : in aquatic 

 Pulmonata it may consist of more than one piece, and in a few terrestrial forms it 

 is absent, e. g. Testacella. 



The salivary glands vary in form and size in different Pulmonata. They are 

 compound glands, but the ultimate acini are composed of a number of uni- 

 cellular glands. They receive bloodvessels and nerves, the latter from the buccal 

 ganglia. An additional salivary gland lies imbedded in the buccal mass in Helix 

 pomatia round the entrance of the main salivary ducts. It consists of unicellular 

 glands, partly opening into the salivary ducts, partly uniting and opening by ducts 

 of their own into the oral cavity. The salivary extract converts starch into sugar. 

 The muscular coats of the digestive tract are an external circular, and an internal 

 longitudinal coat. The longitudinal ridges of the internal surface are formed by 

 the longitudinal muscles. The epithelial cells possess a cuticle, and cilia are 

 present in places ; in young Helices over the whole surface of the stomach. Goblet 

 cells are present in Zonites and apparently in Helix; and in the former Nalepa 

 observed small cells at the base of the other cells, which they are apparently 

 destined to replace. The liver or hepato-pancreas is a compound acinous gland. 

 Its acini are held together by connective tissue, ramifying bloodvessels and nerves. 

 The epithelium forms a single layer. In the ducts are found columnar cells, 

 sometimes ciliated, but not in H. pomatia (Barfurth), as well as mucous-cells : in 

 the acini three kinds of cells liver-cells (Barfurth) or granular-cells (Frenzel); 

 ferment-cells (Barfurth), club-cells, or club-shaped ferment-cells (Frenzel); and 

 calcareous-cells. The granular cells contain each a vesicle which incloses a number 

 of more or less coloured highly refractile granules, fat globules variable in size, 



1 The character of the dentition is especially useful for classificatory purposes in the Azygo- 

 branchiate Gastropoda. The names in use are chiefly the following. The formulae indicate the 

 presence or absence of median, admedian, and in Rhipidoglossa of lateral teeth. Rachiglossa, o. I. o, 

 e.g. Volutidae: Hamiglossa, T. i. i, e.g. Murex, Buccinum'. Toxoglossa, I. o. i, e.g. Conidae: 

 Taenioglossa, 3. i. 3, e. g. Cerithium, Natica, Littorina, Paludina : Cteno- or Pteno-glossa, oo. o. oo , 

 e. g. lanthina : Rhipidoglossa, oo. 4-7. i. 4-7. oo, e. g. Turbo, Nerita (also Haliolis, Fissurella, among 

 Zygobranchiata). There are forms of dentition which do not fall under any of the above-written 

 terms, e.g. Patella Vulgata, the Limpet, with 3. I. 4. i. 3. 



