THE CRUSTACEA 



and thickened, and to this the egg-masses are attached between 



the valves of the shell. 



As regards the homologies of the parts of the Branchiopod-limb 



with those of the biramous type found in other Crustacea, two 



views have been suggested. 

 According to the interpreta- 

 tion adopted by Huxley, 

 among others, the " flabel- 

 lum " or distal exite of the 

 Apus-limb corresponds to the 

 exopodite, while the distal 

 part of the corm represents 

 the endopodite. Lankester, 

 on the other hand, considers 

 the endopodite and the 

 exopodite to be represented 

 by the fifth and sixth 

 endites respectively, the 

 corm being the protopodite 

 and the flabellum the epi- 



The former view 



br 

 Fio. 25. 



Eleventh trunk-limb or oostegopod of Ajnts caneri- I 



formis, female. (After Lankester.) 1-6, the six endites, ig sUDDOrted bva Comparison 

 of which the sixth is fused with the " sub-apical lobe " . rr . / ... \_ 



which forms the pouch, p, containing the eggs; fl, With the leai-llKC thoracic 



the cover of the pouch; br, the limbg of the Leptostraca) 



rg while Lankester's interpreta- 



tion is based chiefly on a comparison of the pre-oral with the post- 

 oral appendages in the larval Apus, and of the trunk-limbs of Apus 

 with the maxilla and maxillipeds of various Decapods. Neither 

 view is quite free from difficulties, and the 

 divergences in structure mentioned above 

 as occurring in the Anostraca still further 

 complicate the matter, which requires 

 further investigation. 



Alimentary System. The oesophagus is 

 narrow and is provided with constrictor 

 and dilator as well as longitudinal muscles. 

 It usually projects a little way into the 

 more capacious mid-gut, and in Polyartemia 

 the terminal part is armed with setae. 

 The hind-gut is short and muscular. In 

 the aberrant Cladoceran Leptodora the 

 oesophagus is of great length and the 

 mid -gut hardly extends in front of the diverticuium. 

 terminal segment of the body. In many 



Cladocera belonging to the families Lyncodaphnidae and Lynceidae 

 the mid-gut is more or less coiled, forming a simple loop or a spiral 



Fio. 26. 



Plniroxus uncinatus (Cladocera) 



