igo8.] R. E. Li'OYD : Bathynomus giganteus. 89 



smaller Isopods has attracted the attention of several histologists (7,8, 14-17). All 

 agree that two kinds of cells are apparent in the walls of these tubular organs, a large 

 sort which projects into the lumen and a small sort which does not; but the majority 

 of observers hold that the smaller kind is merely the young stage of the larger. The 

 smaller cells, when examined in the fresh condition, always show a dense mass of 

 spherical yellow granules surrounding the nuclei. These granules are generally 

 spoken of as zymogen : in some circumstances and in a somewhat capricious manner 

 they readily take up stain. Their behaviour to reagents is given in detail by 

 Murlin. There can be little doubt that the granules, which are shown aggregated in 

 figure I , more detailed in figure 2 , are of a similar nature. 



Examination of the hepatopancreas of Bathynomus therefore shows, that whereas 

 the gross structure of this racemose organ is quite different from that of the simple 

 tubular glands of smaller Isopods, there is a close similarity in cell detail between the 

 two. In another respect there is a similarity and a difference. The hepatopancreas 

 of Bathynomus has, deep in its substance, well-developed strands of muscle fibres ; 

 these strands lie between the radial tubules ; they must be homologous with the bands 

 of muscle fibres, present in the smaller Isopods, which take a spiral course and give to 

 the organ its characteristic twist. 



Minute Structure of the Alimentary Canal. 



The text -figs. 2 — 4 represent sections of the several parts of the alimentary canal. 

 Each of them was drawn, magnified to the same degree, by means of the camera 

 lucida; hence the proportional thickness of the organs is accurately shown in the 

 figures. 



The wall of the gizzard is only about -15 mm. in thickness throughout most of its 

 extent; more' than half of the thickness is due to an outer layer of fibrous material, 

 which does not stain readily, and closely resembles in its histological detail the cornea 

 of a mammal. The inner part of the wall is composed of an epithelial layer in which 

 round nuclei, situated at regular intervals but not separated by cell outlines, are a 

 conspicuous feature. This endothelial layer supports a cuticular ''intima" which 

 varies much in thickness throughout the gizzard. Between the outermost layer 

 and the endothelium is a narrow, fibrous-looking layer which stains deeply, the exact 

 histological character of which was not understood ; it is separated from the epithelium 

 by a narrow homogeneous layer which appears to be a "basement membrane" for the 

 endothelium. 



The structure of the mid gut is now to be considered. As mentioned before, 

 the endothehum is relatively of great thickness and is convoluted to a remarkable 

 extent. The convolutions take the form of alternate ridges and furrows, the axes of 

 which are somewhat irregular in position, but are, on the whole, set longitudinally. 

 The whole thickness of the wall is about i millimetre : about i^oths of this is 

 composed of the endothehum, while the remaining -^(,-th is made up of a few inner 

 circular and outer longitudinal muscle-fibres. The fissures between the ridges extend 

 nearly as far as the muscular layer. Each ridge is composed of a thick outer layer of' 



