i 94 DISCOVERY REPORTS 



remains of five other examples of Pleuromamma sp.,. . .in addition there were three 

 examples of Heterorhobdus belonging to two different species". Still another specimen 

 contained the half-digested remains of a small fish, among which the fin rays and noto- 

 chord were easily identifiable. These specimens — Sagitta, free-swimming copepods, 

 young fish — are all active animals, and yet Gigantocypris can and does catch them. 

 This is especially remarkable in the case of the Copepods, for these have a very rapid 

 escape reaction — at any disturbance they dart away at an extremely high speed. 



There are thus two facts to be reconciled, first, that Gigantocypris is sluggish in its 

 habits and incapable of rapid movement, and second, it feeds on most active prey. 

 I can only suggest that it is on the whole a sedentary feeder, waiting for food to come to 

 it and catching it as it passes by, more in the manner of a sessile animal. But this 

 involves very active mouthparts for, as I have already explained, the valves of the shell 

 cannot be opened, and the only passage to the mouth is through the small opening at 

 the confluence of the antennal notches. If a particle drifts by this opening, or if live 

 prey swims by, it can be grasped in the usual Cypridinid manner by the mandibular 

 palps on either side of the mouth. But the mouth and the mandibular palps may be well 

 inside the shell, and hence there must be a mechanism whereby the mouthparts can 

 be pressed downwards on to the antennal notches so that the mandibular palps can be 

 thrust out. This is made possible, I believe, by the peculiar criss-cross musculature 

 of the dorsal body wall of the trunk region. In Doloria I suggested (1931, p. 448) that 

 the " . . .function of moving the body fluids. . .must be the main function of the dorsal 

 body wall . . . ". In Gigantocypris I have been able to substantiate this point much more 

 fully and consider that this movement of body fluid leads to a movement of whole 

 parts of the body, and that it is by this means that the mouth region is brought up 

 against the ventral slit during feeding. 



Before discussing in detail the skeletal adjustments controlled by this hydrostatic 

 system there is a view, in my opinion erroneous, of the constitution of the main body 

 of Gigantocypris which must be mentioned. The space inside the hollow spherical shell is 

 almost filled by the body of the Gigantocypris (Fig. 1 ; Plate XXXIX, fig. 1). The greater 

 part of this body — the posterior part — is itself spherical and concentric with the shell. 

 Now Miiller (1895, p. 156) and Liiders (1909, p. 105) both maintained emphatically 

 that this distended body is a sac full of blood, or at least contained a marked pre- 

 ponderance of blood over the other tissues. This is, I think, the general opinion 

 concerning those planktonic forms which have adopted a spherical shape, or, in com- 

 parison with their near relatives, are in a distended condition, such forms as Mimonectes 

 and Nebaliopsis. In Gigantocypris, however, this is not so. The posterior part of the 

 body contains a large gut, always laterally compressed, even when distended with food 

 remains. Between this gut and the dorsal and lateral body walls there is a large mass of 

 gut parenchyma, arranged in the typical Cypridinid manner, that is, as a thick layer 

 completely covering the gut and stretching to the dorsal and lateral body walls as 

 several longitudinal ridges. In between these ridges there is fluid — blood — but, by 

 comparison with sections of other Cypridinids, it is clear that this is not present in any 



