FEEDING-MECHANISM 3 i 9 



was swimming, became trapped in the sticky secretion of the marginal glands of the carapace. He 

 observed this to be drawn in by the mandibular palps and formed into a mass by the mouth-parts. 

 He pointed out that this process took place whether anything was trapped in the secretion or not. 

 Elsewhere (p. 127) he stated that he was not able to observe directly that it was swallowed, but found 

 that the stomach contents were similar in nature to this material. It is perfectly clear, from the structure 

 of the mandibular palps, that they could draw in the secretion of the marginal glands from the front 

 half of the carapace, as observed by Muller. The apical claws are suited to such function (Fig. 2), 

 while the posterior marginal setae and possibly also the anterior marginal setae could contribute to the 

 process. Muller (1894) held the view, repeated by Caiman (1909), that the greater development of the 

 anterior marginal glands of the carapace may be associated with this process. It is not, however, 

 universally true that these glands are better developed than the others. In fact, if anything, Conchoecia 

 antipoda has them less well developed. It would be possible, however, for the secretion from the more 

 posterior parts of the ventral margin to be drawn forwards by the anterior curving claws of the 

 maxillary exopod ( Fig. 2) . The possibility of the limb moving in this fashion has already been considered 

 (page 316). The secretion could thus be brought within range of the movement of the claws of the 

 mandibular palps and added to any food collected directly by them. The only appendages which can 

 reach the posterior margin of the carapace, which is also provided with numerous glands, are the 

 second trunk-limbs. Their fine setae are poorly adapted to movement of such material, while their 

 range of movement could hardly bring it within reach of other appendages. Thus although food- 

 material may be trapped by secretion from the glands of the carapace, these cannot be entirely sub- 

 servient to this function. 



The structure of the appendages shows that Midler's statement, that food-laden secretion dragged 

 in by the mandibular palps is passed into the oral atrium by the palps of the maxillule, probably does 

 not cover the whole process. It is improbable that the movement of these structures would be sufficient 

 to pass material directly into the oral atrium. When the mandibles are folded under the body, their 

 claws extend into the field of movement of the maxillary endopods (Fig. 7) which with their back- 

 wardly curved claws could easily withdraw material from the mandibular claws. The maxillulary 

 palps, with their forwardly curved claws could then draw food-material forward from the maxillary 

 endopods to bring it below the labrum in the region of the mandibular gnathobases. 



The other possible method of collection of fine material is quite different. I have frequently noted 

 that preserved material may have a mass of detritus held beneath the labrum by the open cage of setae 

 formed by the infolded mandibular palps. This could of course have been passed forward by the 

 maxillulary palps, and could also be contained in the secretion from the marginal glands of the cara- 

 pace, which has been swept in by the posterior marginal setae of the mandibular palps. There is, 

 however, another possible explanation for the presence of detritus in this region. The beat of the 

 epipods of the maxillules and maxillae creates a water-current through the carapace, and will carry 

 detritus with it. Muller (1894) has, indeed, described how detritus is carried in this manner in the live 

 animal. A large part of the water-current must flow between the mandibular palps and over the 

 surface of the labrum in just that region where the numerous openings of the anterior labral glands 

 are situated. This resembles the food-collection mechanism described by Graham Cannon (1933) in 

 Cypridina. There is no information available regarding the nature of the secretion of the labral glands 

 in Conchoecia but, if it is comparable with that of other Crustacea, it will be a sticky secretion which 

 will entangle any detritus swept in with the water-current, as in the case of Cypridina. The secretion 

 together with the detritus would then be held in place by the marginal setae of the mandibular palps 

 and be available as a source of food-material. Whether detritus is collected in this manner beneath 

 the labrum of Conchoecia as food-material can only be determined experimentally. 



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