igoS.] 



R. E. L-iyOYD : Bathynomus gig aniens. 



83 



organ and the body wall. These tubes are composed of few but large cells arranged 

 in one layer. In Asellus there are only about ten rows of cells, in Porcellio there 

 are not more than twelve. If this plan of organisation, which is shown in text-fig i, 



were to be exactly reproduced in an 

 Isopod of 20 cms. in length, the indi- 

 vidual cells of the tubules would be 

 at least 5 mm. in length. We should 

 not expect to find this. If, on the 

 other hand, the cells of the tubules 

 were increased in number but not in 

 size, the lumen of the tubule would 

 be of disproportionate dimensions. 

 Such a cavernous organ could not 

 well perform either of the functions 

 of a hepatopancreas. We should 

 expect, therefore, in Bathynomus, 

 either that the tubules would be 

 very largely increased in number, or 

 that they would be replaced by com- 

 pound glands of a racemose nature. 



The Alimentary System. 

 The alimentary canal, as in 

 other Isopods, can be at once divided 

 into three divisions, — the fore gut, 

 midgut, and hind gut. But whereas 

 in the small Isopods the hind gut is 

 of insignificant length and the mid 

 gut composes at least three quar- 

 ters of the whole canal, in Bathynomus the length of the hind gut is greater 

 than that of the fore and mid gut together. It will be seen later on that there is 

 some doubt as to whether the three divisions of the gut are homologous in both cases. 



The fore gut {pharynx). ' 



In describing the buccal orifice, M. Bouvier mentions its cleft-like character and 

 describes two projecting processes at the anterior and posterior ends of this aperture. 

 The anterior of these is much the larger, but internal examination shows that it is 

 continued into the roof of the pharynx for a short distance only, whereas the smaller 

 posterior one becomes more prominent as it ascends into the pharynx. In a trans- 

 verse section of the middle of the pharynx, this ridge is the only prominent feature ; 

 it comes to an end in the gizzard. The pharynx lies in a position half-way between 

 the vertical and the horizontal. Its length is about 10 mm. In transverse section 

 it measures 6 mm. in the longitudinal axis, 4 mm. in the transverse. It is lined 



Fig. 



