84 Memoirs of the Indian Museum. [Vol. I, 



by a tough cuticle of a dark brown colour, which is folded in a somewhat irregular 

 manner ; the only definite fold being the trenchant ridge on the posterior or ventral 

 side. 



Fore gut {gizzard). 



This is a complex organ, and although at first sight it seems to differ consider- 

 ably from the same structure in the small Isopods, consideration shows that the 

 component parts are homologous in the two cases. The gizzard is sharply marked 

 off from both pharynx and mid gut. In form, it is an elongated, polygonal solid, 

 measuring 19 mm. in length and 9 mm. in breadth. It lies almost entirely within 

 the head. In the natural position, the posterior third of the gizzard cannot be seen 

 from above, since the anterior end of the mid gut protrudes over it as a blind pouch. 

 Below it rests on a skeletal plate, part of the internal skeleton of the head which 

 will be described later on. The outward form of the gizzard is shown in figures 

 5 and 7, pi. xi. From whatever side the organ is examined, its wall exhibits deep 

 grooves or furrows : these are the outward expressions of certain involutions of the 

 gizzard wall, which have become thrust into the cavity. 



On opening the gizzard, these involutions are seen to have almost abolished the 

 cavity, which is reduced to a number of small crevices between them. The form and 

 position of these involutions is best studied by examining the interior of the organ, 

 after it has been divided by a longitudinal section in the middle line. Figure 8 

 shows the appearance of the inner surface of one half of the organ, after such a divi- 

 sion. The most prominent features are two large ampullae situated one in front of 

 the other {a. a., p.a.); the anterior of these is the smaller, but seems to be functionally 

 the more important, as most of its outer or concave side gives attachment to a large 

 muscle ; whereas the larger and posterior one is an empty cavity (fig. 6) , in the dead 

 specimen, being lined merely by a thin layer of white fatty material. 



In its posterior third, the roof of the gizzard is involuted along two oblique 

 converging lines, the results of which are seen internally as two long, smooth pro- 

 cesses, u.V. p., projecting downwards and backwards, one on either side of the median 

 plane and almost in contact with one another. The principal part of the opening 

 from the gizzard to the mid gut lies between these two processes They appear to 

 have a valvular function, to prevent regurgitation from the mid gut. They contain 

 a basis of fatty material and are covered with a smooth, thick cuticle. They are 

 7 mm. in length and have acutely pointed ends. 



The floor of the gizzard also exhibits some important structures. In its posterior 

 third, on either side of the middle line, is an elevated ridge with a falciform and 

 trenchant margin ; this is shaped posteriorly so as to act as a lower valvular process, 

 l.v.p. In about the middle third of the floor of the gizzard is another somewhat 

 similar pair of ridges; these are distinct from the others but overlap them slightly. 

 They are very hard, especially on their median surfaces, which are in contact. The 

 cuticle of these surfaces is yellow and shining in contrast with the rest of the lining 

 of the organ, which is greyish white. 



