438 DISCOVERY REPORTS 



In following out the musculature I found the use of polarized light to be of great 

 assistance. (For details see p. 447.) 



The figures in Plate VII are of colour photomicrographs taken by the Lumiere 

 process. Their colouring is fairly accurate, but not as brilliant as in the original pre- 

 parations, 



FEEDING MECHANISM 



The feeding mechanism of Doloria may be deduced from a comparison of its body 

 shape and limb arrangement with those of Pionocypris vidua, whose feeding habits I 

 have described from direct observation (1926 a). 



The form of the body is shown in Fig. 2 and Plate VI. It shows a marked difference 

 from P. vidua. In the latter, the mouth is brought to the level of the edges of the valves 

 by the large oral mass consisting of the labrum and hypostome (Fig. i). In Doloria 

 the mouth is well inside the valves. The labrum is large but the hypostome is a flat, 

 quadrangular plate, forming the hinder margin of the mouth. 



The shell cavity, as in all Ostracods, is divided effectively into two chambers by the 

 attachment of the body to the valves. This runs dorso-anteriorly from the attachments 

 of the adductor muscle (Fig. 2), as a narrow isthmus, and spreads out fore and aft in 

 the region of the heart. The space in the dorsal part of the anterior chamber is almost 

 filled, laterally by the paired eyes, the antennules and the enormous basal joints of the 

 antennae, and medially by the nauplius eye and frontal organ. Below these, the labrum 

 projects downwards in the middle line. Close against its sides, overlapped by the 

 antennae above and projecting forwards in the same relative position as the mandibular 

 palps of P. vidua, are the mandibles (Plate VI). The mandibular exopodite forms a 

 small claw on the "knee" and there is no vibratory plate. The maxillules project 

 antero-ventrally at the level of the mouth, their tips working together in the middle 

 line just below the latter. Close behind and parallel with the maxillules are the maxillae 

 with their vibratory plates guarding the entrance from anterior to posterior chamber. 

 The first trunk limbs form two setose triangular plates, parallel and lying close to the 

 median plane between the maxillae. The second trunk limbs, the "bottle brush" 

 limbs, project dorsally into the posterior chamber. 



The posterior chamber serves as a brood pouch. In the ripe female it is almost filled 

 by the posterior part of the body. The latter ends in a powerful caudal furca which 

 may project from the shell (Plate VI), or may be flexed up between the first trunk 

 limbs, thus reaching forwards to the level of the mouth. 



The similarity between the arrangements of the body in Doloria and in Pionocypris 

 and the similar structures, not necessarily homologous, which occupy analogous posi- 

 tions in the two chambers of the shell, I consider suggest very strongly that the principle 

 of the feeding mechanism is the same in the two forms. 



The vibratory plate of the maxilla, in its oscillation, must paddle water out of the 

 posterior opening of the shell, and, since this plate spans completely the junction of 

 the two chambers (Plate VI), the water must be sucked in at the anterior end of the 



