42 



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 

 Afn8^\vo\i 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- 

 podite. The former view 

 is supported by a comparison 

 with the leaf -like thoracic 

 limbs of the Leptostraca, 

 while Lankester's interpreta- 

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

 oral appendages in the larval Afus, and of the trunk-limbs of Apis 



with the maxilla and maxillipeds of various Decapods. Neither 



A'iew is quite free from difficulties, and the 



divergences in structure mentioned above 



as occuri'ing 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 



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 



Fig. 25. 



EleviMitli trniik-limb or oostegopod of A-pvs eancri- 

 /oriiiis, female. (After Lankester.) 1-6, the six endites, 

 of which the sixth is fused with the " sub-apical lobe " 

 which forms the poucli, p, containing the eggs ; fl, 

 flabellnm forming the cover of the jjoueh ; 6)-, tbe 

 vestigial bract. 



Fig. 26. 



Pleuroxns vnciimtvs (Cladocera) 

 (after Lilljeborg), showing the 

 coiled intestine and its vential 

 diverticulum. 



