ENTOMOSTRA CA. 



265 



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

 are without palps, and the maxillae 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. 

 Artemia. 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. milhattsenii, and 



vice versd. Artemia 



fertilis 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 heimaphrodite. 

 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 

 foim, 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. 1 13.- -Dorsal surface of Apus 

 cancriformis. — 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. 



Oral. 



1. Antenna. 



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



apparently always in certain species. ) 



3. Mandible. 



4. Maxilla. 



5. Maxillipede. 



