BRANCHIOPODA 355 



which each pair starts a little earlier than the pair in front of it, they 

 cause, bya pumping action which shall be described presently(p. 358), 

 a flow of water into the median gully whose sides are formed by the 

 two rows of limbs, thence outwards into the spaces between each 

 limb and its neighbours in front and behind, and then backwards. 

 This current brings with it the particles which serve for food, bathes 

 the branchiae, and causes, in the Anostraca and Notostraca, forward 

 movement of the body. As the water passes outwards, the food 

 particles are, by the bristles on the endites, strained off and retained 

 in the median gully. The apparatus varies in detail with the nature 

 of the food. In the Notostraca, which feed mainly by stirring up, 

 with the tips of their thoracic limbs, detritus on the bottom and then 

 filtering it, the bristles on the endites are not adapted to straining 

 out fine particles (which therefore escape with the outgoing current) 

 but detain coarser particles. This is perhaps the primitive mode of 

 feeding of the Branchiopoda, and may even be inherited from the 

 Trilobites. In the Anostraca and Diplostraca there is a special ap- 

 paratus for filtering off fine particles. This consists of a close set row 

 of long, finely feathered setae, placed on the edge of the endites and 

 so disposed as to cover the opening from the median gully to the space 

 between the limb and its neighbour behind. Members of these orders 

 which derive part or all of their food from detritus have various kinds 

 of apparatus, composed of bristles, for removing the coarse particles 

 and passing them backwards to be either swept away with the out- 

 going stream or broken up for food by the hinder members of the 

 series of limbs. Finally, the material gathered is passed forwards to 

 the mouth in a median "food groove" along the belly by a current 

 whose causation is a matter of dispute. The feeding apparatus whose 

 principles have just been described differs greatly in detail in different 

 branchiopods, and reaches its highest complication in the tribe of 

 cladocera known as Anomopoda, to which the common water-flea 

 Daphnia belongs. Examples of it are described more fully below. 



The Gymnomera have slender, mobile, jointed trunk limbs with 

 which they manipulate the relatively large organisms which serve 

 them for food. 



The telson is in the Anostraca subcylindrical, with the caudal rami 

 as elongate plates or styles ; in the Notostraca it has the rami long and 

 many-jointed, and is in Lepidurus produced backwards on the dorsal 

 side as a plate. In the typical Diplostraca it is flexed ventrally and 

 produced backwards laterally into a pair of strong, curved, toothed 

 claws, and can be brought forward ventrally to clear the gully between 

 the limbs. In the Gymnomera it has re-straightened. 



The compound eyes are in the Anostraca stalked (in Lepidocaris they 

 appear to have been absent). In the remainder of the class they are 



