GIGANTOCYPRIS MtJLLERI 235 



by a normal Cypridinid in the excessively rapid escape reaction that it shows when 

 disturbed. In Gigantocypris there are no giant fibres extending outside to the muscles 

 of the antennae — or in fact anywhere else — but then Gigantocypris can have no escape 

 reaction. Its size and shape preclude that. The movement of an ordinary Cypridinid 

 in swimming away from a disturbance is as rapid, if not more so, than that of a Copepod. 

 Clearly, as I have pointed out previously, the body of a Gigantocypris could not possibly 

 move itself through the water with any speed. Hence the absence of the giant fibre 

 system. 



These observations support very strongly what a cursory survey of the animal kingdom 

 shows, namely, that all those animals where a giant fibre system is known to be present 

 show a definite escape reaction. The earthworm, tubicolous worms and the crayfish 

 are three obvious examples. A giant fibre system, therefore, appears to be a nervous 

 mechanism which has evolved to co-ordinate escape movements. 



EXCRETORY ORGANS 



The segmental excretory organs of Gigantocypris are antennal glands (Cannon, 193 1, 

 p. 478). They have the same gross anatomy as those of Doloria, each consisting of 

 a simple end sac, an efferent duct and a "sphincter" guarding the entrance into this 

 duct from the end sac. 



The whole gland is situated in a posterior thin walled bulge on the basis of the antenna. 

 The duct opens as in Doloria on the outer side at the junction of this thin walled lobe 

 and the more anterior thick walled muscular part. It consists of two distinct portions — 

 distally a tubular invagination of thickened ectoderm and proximally an intracellular 

 duct formed by three cells only. That there are only three cells in this latter part of 

 the duct was established from the sections of an embryo which has been mentioned 

 previously. Here the developing duct had the same appearance as in other intra- 

 cellular ducts that I have studied. The width of the lumen was approximately the same 

 as the thickness of its walls and the nuclei were at least twice the volume of the sur- 

 rounding nuclei. In the adult, however, the cells appear to have the actual shape of an 

 agricultural drain-pipe — that is of a relatively thin walled hollow cylinder. The nucleus 

 of the individual cells bulges into the lumen and not to the outside as might be expected 

 (Fig. 176). 



These duct cells lie close against the lateral ectoderm of the basis of the antenna and 

 are connected to the ectoderm by ordinary connective strands (Fig. iyb). On the inner 

 surface, however, they are covered by a simple epithelium of exceedingly thick cells 

 which appear glandular. The proportion between these cells and the duct cells proper 

 is such that at first sight it looks as though the duct cells merely form the peripheral 

 layer of the gland cells. From the section seen in Fig. iyb, however, it is clear that the 

 duct cells are quite distinct from the overlying gland cells. The latter, if they are in fact 

 glandular, pass their secretion outwards into the cavity of the limb and not into the 



duct of the gland. 



7-2 



