20 W. BALDWIN SPENCER. 



layer, which is well developed, and consists for the greater 

 part of fibres running, some obliquely round the oesophagus, 

 others parallel to its length. Just beneath the stomach wall 

 a ring of circularly disposed fibres is present (fig. 50, M.CE.), 

 which acts as a sphincter. The opening into the ventral 

 wall of the stomach is placed some little distance posteriorly 

 to the anterior end of the latter. The oesophageal tube 

 pierces the wall, and the columnar epithelium rises up into a 

 most distinct papilla. On this a funnel-shaped opening is 

 present, leading into the oesophagus, and the epithelium ap- 

 pears as it were to flow over the margins of the funnel, and 

 then to dip down all round under the epithelium of the mid- 

 gut. The papilla is lined all over by a thin layer of cuticle, 

 and just at its base the cavity of the oesophagus always swells 

 out to form a space of the characteristic form shown in 

 fig. 50. 



(4) Stomach or Mid- gut. — This forms a straight tube 

 which runs directly from about the level of the mouth to 

 within a short distance of the very posterior end of the body. 

 Its average diameter is '83 mm. The walls internally are 

 thrown into well-marked longitudinal folds, and are lined by 

 a single layer of definite columnar cells (fig. 50, M. G. E.). 

 The outlines of these are very distinct, and each contains a 

 spherical nucleus, placed usually nearer to the external than 

 the internal end. The cells rest upon a basement membrane, 

 and external to this lie the muscle layers. The internal one 

 consists of circularly and obliquely disposed fibres, but the 

 more strongly developed is the external one, which consists of 

 longitudinally disposed fibres [M. Al. Long.). Leuckart de- 

 scribed a longitudinal layer of muscles, but their presence is 

 denied by Stiles,^ according to whom this layer is merely a 

 connective-tissue coat. In the form now being described 

 I think there is no doubt whatever as to the muscular nature 

 of this layer. 



There is present in addition a certain amount of material 

 which may be described as connective tissue, and which is 

 ' Loc. cit., p. 124. 



