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such characters as distinguish a cleaning limb from a crawling leg (cf. G. \V. AIÜLLElj, 1894.
pl. 12, fig. 49). If we turn to the family Darwinulidae, which is closelv related to the
C y p r i d s, we find that although the fifth limb has been developed as a presumablv rather
effective masticatory organ, the seventh limb is not differentiated as a cleaning organ but has
entered the service of locomotion. Nor do the conditions in the Cypridinids support
the assumption put forward by G. Alm. The fifth limb in, for instance, the genera Cypridina
and Philomedes certainly helps considerably in breaking up the food, even to a far greater
extent than in so me C y p r i d s ; this idea is supported by the extremely powerful musculature
and armature of this appendage. As in these genera the seventh limb is developed as a
presum-ably effective cleaning organ one would think, of course, that the conditions in these genera
support G. Alm’s hypothesis, but, as we know, the faet is that in these genera the mandible
does not at all help or at any rate only helps very slightly in the breaking up of the food, which
quite makes up for the development of the fifth limb as a masticatory organ. The Asteropids
are characteri zed by a method of taking up the food that is quite unlike that of other
Cypridinids. As we know, a rather strong current of water from front to back is produced in the
Cypridinids by the movements of the vibratory plate on the fifth limb; this is for
respiration — as is generally assumed and appears very probable. \Vhile in most Cypridinids
this stream is allowed to pass freely along between the shell and the body without losing any
of the organic and inorganic little particles that naturally accompany it, whirled up from the
bottom, this is not the case in the Asteropids. As has been described in another place
in this treatise, the limbs of the mouth have been differentiated in a very strange way in these
forms. The maxilla has been developed into a sort of baleen-like organ, which, with its epipodial
appendage and its long, fine ventral bristles filis the anterior opening of the canal through
which the respiratory water has to pass. By means of these baleens the water that runs through
is cleaned of a great many of the defiling particles; a nuinber of these particles constitute the
food of these forms. The water that, after passing the maxilla, continues backwards between
the shell and the wall of the body, is thus presumably much cleaner than the respiratory water
in other Cypridinids. It is true that the fifth limb is developed as a mouth organ in these
forms, but it does not act as a masticatory appendage and thus does not increase the number
of the defiling particles. The food is not broken up at all and the respiratory water that passes
is cleaned from small defiling particles before it penetrates into the part that is cleaned by
the seventh limb. In spite of this this limb is well developed as a cleaning organ in
these forms. The Haloey prids have in their mandible and maxilla quite as powerful
masticatory organs as any representative of the family Cypridae; in addition they have
a rather powerful masticatory part on the fifth limb. In spite of this their cleaning
limb is very much reduced; cf. the remark above, p. 89. Finallv it ought to be noted
that among the families whose fifth and seventh limbs are developed as tvpical crawling
legs there are certainly forms that have more powerful and more intensive mastication
than a number of forms whose seventh limb is developed as a cleaning organ and whose
fifth limb helps more or less in intensifying the mastication. The methods by which
the Cyther, ellids and the P o 1 y c o p i d s take up their food are too little known
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