54- PHYSIOLOGY OF THE INVERTEBRATA. 



narrow conduit running along the ventral side of the trunk 

 between the bases of the legs. The particles are here suc- 

 cessively thrown forward, chiefly by the aid of the coxal lobes 

 of the legs, till they reach the oral region, where they are 

 partly pushed into the mouth by the aid of the maxillee, 

 partly caught by the protracted labrum, and by the retraction 

 of that part brought imniediately within the reach of. the 

 mandibles. When the animal is feeding, the latter organs 

 a,re found to move almost incessantly, their molar surfaces 

 being at short intervals closely applied against each other 

 and their bodies revolved, so as to cross and triturate the 

 particles. At the same time the labrum is lowered at short 

 reprises and then thrown back against the mandibles, thus 

 continually conveying new particles within the reach of the 

 mandibles. The swallowing movements of the oesophagus 

 when transferring prepared food to the intestine, are very 

 distinctly observed through the shell, whereas the intestine 

 itself does not seem to perform any perceptible peristaltie;4 

 movements." ' 



(23) The Cladoccra. — In this order, to which Daphnia 

 belongs, the alimentary canal does not differ very much from 

 that of the Pliyllopoda. Many of the Australian Gladocera 

 have been recently investigated by Dr. G. 0. Sars.* In 

 Z'atonopsis australis, Simoceplialus cmstraliensis, MacrotlvitK 

 spinosa, and Ilyocryptus Imigiremis, the alimentary canal is a 

 simple tube traversing the body, whereas in .DunJievedia crassa, 

 and Alona archeri the alimentary canal forms in the middle 

 of the body a double loop before passing to a dilatation in 

 front of the muscular rectum. A large dilatation or sac is 

 also present in Ilyocryptus longireviis, but there are no loops. 

 A sac of smaller size is observable in all the above-mentioned 

 fprpis, and is situated in each case in front of the rectum. 

 The intestine or alimentary canal of Maerothrix spinosa is 

 dilated in its anterior part ; an:d the' digestive tube of Simo^. 

 oephalus australiensis is provided with two large incurved 

 * Chriatiar.ia Videnslahs — SeUkahs Forhandlinyer, 18S8, No. 7. 



