ENTOMOSTRA CA. 



285 



First Sub-Class. ENTOMOSTRACA. 



Order I. Phyllopoda. In these at least four pairs of swimming feet 

 bear respiratory plates. The body is generally well segmented, 

 and is protected by a shield-like or bivalve shell. The mandibles 

 are without palps, and the maxillte are rudimentary. 

 (a) Branchiopoda. The body has numerous segments and (10-20 

 or more) appendages with respiratory plates. The shell is 

 rarely absent, usually shield-like or bivalved. The heart is a 

 long dorsal vessel with numerous openings. The eggs are able 

 to survive prolonged desiccation in the mud. 



BranchipuS) a beautifully coloured fresh-water form, with 



hardly any shell. 



Artcinia. Brine-shrimps. Periodically parthenogenetic. By 

 gradually changing the 

 salinity of the water, 

 Schmankewitsch was 

 able, in the course of 

 several generations, to 

 modify A. salina into 

 A. inilhaitscnii, and 

 vice versa. Arteinia 

 fcrtilis is one of the 

 four animals known to 

 occur in the dense 

 waters of Salt Lake. 

 Apus, a fresh-water form 

 with a large dorsal - 

 shield. Periodically 



parthenogenetic. One 

 species hermaphrodite. 

 Of these, Apus is certainly the 

 most interesting. It is over 

 an inch in length, and 

 therefore a giant among 

 Entomostraca. It has an 

 almost world-wide distribu- 

 tion. " It possesses peculi- 

 arities of organisation which 

 mark it out as an archaic 

 form, probably standing 

 nearer to the extinct an- 

 cestors of the Crustacea 

 than almost any other living 



member of the group." The appendages are very numerous and 

 mostly leaf-like. They may be regarded as representing a 

 primitive type of Crustacean limb. Professor Ray Lankester 

 enumerates them as follows : 



FIG. 136. Dorsal surface of A/>us 

 cancrifonnis. - - From Bronn's 

 " Thierreich." 



In the anterior region are the two com- 

 pound eyes, and behind them the 

 simple unpaired eye. The whip-like 

 outgrowths of the first thoracic ap- 

 pendage project laterally. 



Pre-oral. 



j I. Antenna. 



- 2. Second antenna. (This is sometimes absent, 

 apparently always in certain species.) 



and 



