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 

 Apns-\im\) 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 

 Fio 25 and the flabellum the epi- 



Eleventh trunk-limb or oostegopod of Apus cancri- Pdite. The former V16W 



formis, female. (After Lankester .) 1-6, the six endites, i s supported by a Comparison 

 of which the sixth is fused with the " sub-apical lobe . * * ~ , , 



which forms the pouch, p, containing the eggs; fl, With the leaf -like thoracic 



flabellum forming the cover of the pouch; br, the T i r it. T 



vestigial bract. 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 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 Polyartemiii 

 the terminal part is armed with setae. 

 The hind-gut is short and muscular. In 

 the aberrant Cladoceran Leptodora 

 oesophagus is of great length and 

 mid -gut hardly extends in front of 

 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 



the 

 the 

 the 



Fio. 26. 



Pleuroxus u ncinatus (Cladocera) 

 (after Lilljeborg), showing the 

 coiled intestine and its ventral 

 diverticulum. 



