GIGANTOCYPRIS MOLLERI 2 oi 



The ventral framework to which all the limbs are articulated is built up on a chitinous 

 plate situated immediately behind the mouth, the extent of which can be seen clearly 

 in the semi-diagrammatic view of the ventral skin of Doloria levis (Cannon, 193 1, p. 443, 

 fig. 3). It is a quadrangular plate. Its front edge is the hind wall of the mouth (Plate XL, 

 figs. 2, 8). Its hinder margin is formed by the two first trunk limbs which come close 

 together in the middle line. Laterally, in emarginations on either side, are the three 

 limbs, mandibles, maxillules and maxillae. The plate itself is not very substantial — it is 

 its margins that are thick and stain deeply. It extends forwards round the sides of the 

 mouth and continues as a deep band, the upper labral loop, around the upper half of 

 the labrum and bears at its middle point a frontal knob (Fig. 4). This is a useful landmark 

 in comparing the nauplius eye regions of Gigantocypris and Doloria. From the sides 

 of the mouth there articulates ventrally the helmet-shaped armature of the lower part 

 of the labrum. This lower armature is supported at its upper margin by a powerful 

 sclerite system in the form of a complex loop, which I described in Doloria as the 

 equatorial loop. Between this loop and the frontal knob is thin flexible cuticle (Figs. 3-5). 

 This and the articulation at the sides of the mouth permit of the labrum being raised 

 and enlarging the mouth entrance. The muscles effecting this can be seen in the 

 photograph (Plate XLI, fig. 3). 



From the sides of the upper labral loop extend inwards the large antenno-labral 

 apodemes, typical hollow chitinous intuckings. 1 The entrance to the apodeme on the 

 animal's left side can be seen clearly in Fig. 3 between the cut-off antenna and the 

 labrum. These apodemes pass inwards in a postero-median direction (Fig. 6) and attach 

 to the tendon of the adductor muscle. Similarly, from the sides of the mouth a pair of 

 more powerful apodemes extend directly inwards to attach to the same tendon just 

 median to the attachment of the antenno-labral apodemes. These are the anterior 

 hypostomal apodemes (Fig. 6). The ventral framework with its articulated limbs is 

 thus most rigidly connected through this double apodemal system to the adductor 

 tendon, and, furthermore, there is no similar connexion to the valves. The body thus 

 "floats" inside the spherical shell, being held in position by the adductor muscle, and 

 this, I consider, is the main function of the muscle in this genus. As I have already 

 pointed out (p. 192), the valves have fused together to such an extent that it does not 

 appear possible that the ventral unfused margins can be opened and closed. Hence the 

 adductor muscle cannot carry out its normal function, and yet it persists as a com- 

 paratively massive muscle. This is understandable if its suspensory function is considered 

 now as its main function. I do not consider that this is a new function that developed 

 with the evolution of the genus, but rather that in all other Ostracods the adductor 

 muscle has a double function. It has its normal function of closing the two valves, and, 

 in addition, has the suspensory function that I describe here. 



Another connexion of the body framework to the valves does exist through the 

 articulated sclerite system, but this is only rigid in so far as its musculature makes it so. 



1 The hollow nature of these apodemes was made very evident in one series in which the antenno-labral 

 apodeme contained a large number of fragments of radiolarian skeletons. 



