238 DISCOVERY REPORTS 



from an extrinsic triangular system. This anomaly is parallel to the case which we 

 (Cannon and Manton, 1927) pointed out in connexion with the maxillary glands of 

 Chirocephalus and of Cypris. These segmental excretory organs occurring in the same 

 segment of two related forms would normally be classed as homologous, and yet in the 

 one, Chirocephalus, the duct and sphincter are both mesodermal while in the other, 

 Cypris, they are both ectodermal. 



The sphincter cells project into both end sac and duct, but to a much greater extent 

 into the latter. This seems to be a constant feature in sphincters of this type for 

 Vejdovsky (1901) describes such a state of affairs in Gammarus, while we (Cannon and 

 Manton, 1 927) figured it for Anaspides and certain Euphausiacea and Penaeids. Vejdovsky, 

 however, distinguishes between valve cells, which are those projecting into the lumen, 

 and separate external muscular cells. There is no such distinction in Gigantocypris and 

 I have not yet discovered a Crustacean valve in which these two separate elements occur. 



In Gigantocypris the cells protrude as four elongated masses of glandular cytoplasm 

 into the duct (Fig. 17c). In each mass, at the sphincter end, are droplets of secretion. 

 Towards the distal ends these become larger and at the same time less distinct until at 

 the tips of the cells large drops, presumably of this section, appear to be shed into the 

 cavity of the duct. 



The interest in the end sac wall naturally lies in the manner by which Gigantocypris 

 has compensated its excretory surface proportional to its enormously increased volume. 

 At first sight this appears to have been brought about by the development of a labyrin- 

 thine structure. Sections of the adult gland certainly give this appearance. Sections of 

 the embryo, however, show that there is something more. A labyrinth may be con- 

 sidered as derived from a sac which, by the rich development of partitions and trabeculae 

 from its walls, has been converted into a spongy mass traversed by a complex system 

 of "canals" (Caiman, 1909, p. 285). This has certainly taken place in Gigantocypris 

 but previous to this development, which can be considered as a folding of the surface 

 of the end sac, another has taken place which is a pitting of the outer surface of the end 

 sac epithelium. It is this outer surface which represents the effective excretory surface 

 of the end sac. By developing folds in the epithelium or crypts into the outer surface the 

 excretory surface will be increased. In Gigantocypris both these processes have taken 

 place (Plate XLI, fig. 6). 



In the embryo the wall is a simple but very thick epithelium. It is probably syncitial 

 and the nuclei are all arranged against the inner surface (Fig. 17a). The latter is con- 

 tinuous and small so that it forms, as would be expected, a complete wall around the 

 cavity of the end sac. The outer surface of the epithelium, however, is pierced by 

 numerous holes and these lead into crypts which extend into a ramifying system of 

 vacuolar spaces reaching as far as, but not breaking through the inner surface. The 

 labyrinthine structure, as far as the outer surface of the end sac wall is concerned, is 

 thus primarily due to the development of an intracellular system of crypts. That of the 

 inner surface is due to an intercellular system of folds. Whether or not the outer surface 

 also subsequently develops folds it is impossible to say. 



