THE BRANCHIOPODA 



37 



an external membranous lobe is present and was formerly regarded 

 as corresponding to the gill or hrad of the succeeding appendages. 

 For this reason the appendage was regarded as belonging to the 

 series of the trunk-limbs, and was called a "foot-jaw" or "maxilliped." 

 It has been shown, however, by Claus that the so-called "bract" 

 is really a tubular process bearing the external opening of the 

 maxillary gland, and is in no way related to the " bract " of the 

 following limbs. There is therefore no reason to doubt that the 

 appendage is homologous AA'ith the maxilla of other Branchiopoda. 

 It is of interest to notice, in connection with the great reduction of 

 this appendage, that there is, in Ajnis, no separate ganglion in the 

 A-entral nerve-chain corresponding to it, but that the nerves supply- 

 ing it take their origin from the longitudinal connectives between 

 the ganglia corresponding to the maxillula and the first thoracic 

 appendage respectively. 



Fio. 22. 



A, maxillulae, B, maxilla, of Apus cancriformis. (After Claus.) p, the .so-called inner lobes 

 of the niaxillulap, rei)rpsenting, according to Clans, tlie paragnatha ; o, opening of maxillary 

 gland on a tubular process connected with the maxilla. 



The trunk-limbs of the Branchiopoda are generally of very 

 uniform structure, and are not grouped into definite "tagmata." 

 On the other hand, these appendages present very great differences 

 in the different groups composing the sub-class, and it is not easy 

 in some cases to determine the exact homologies of the various 

 parts. 



The most primitive form is probably that found in the Xoto- 

 straca {Apus, Fig. 23, A). Each appendage consists of a flattened 

 corm or axis to which are attached eight lateral processes or lobes. 

 Six of these processes spring from the inner margin of the corm and 

 are termed endite.% while two on the outer margin are termed exites. 

 The proximal endite (1), placed near the attachment of the limb "to the 

 body, is armed with strong spines and, like some or all of the other 

 endites, is provided with special muscles which permit 'of a limited 

 amount of movement on the corm. These basal endites working 

 against those of the opposite side function as jaws, seizing and 

 passing forward towards the mouth particles of food which are 



