PniLLOPODA. BEANCHIOPODA. 419 



The alimentary canal is provided with two lateral hepatic appen- 

 dages, which are, as a rule, branched and racemose and only excep- 

 tionally short and simple. The heart appears as an extended dorsal 

 vessel with numerous paired lateral slits, and may extend throughout 

 the whole length of the thorax and abdomen (Branchipus). The 

 genital organs, which are always paired, are placed by the side 

 of the alimentary canal, and open at the boundary between the 

 thorax and abdomen. In the females the genital openings are small 

 slits ; in the male there may be protrusible copulatory organs at the 

 openings (Branchipus}. 



The males are distinguished from the females principally by the 

 fact that the anterior, or two anterior pairs of legs, are armed with 

 hooks (Ustkeridce), or by the modification of the posterior antennae 

 to form a prehensile apparatus (Branchipus). Hemarkable is the 

 rare occurrence of the males ; they seem only to appear under certain 

 conditions and in definite generations, which alternate with parthe- 

 nogenetic generations. The eggs during development are generally 

 protected within the body of the mother, and are carried about either 

 in a saccular brood-pouch of the abdomen or between the valves of 

 the shell on filiform (Estheria, Branchipus), or in vesicular (Apus) 

 appendages of different pairs of legs (9th to llth). Tho eggs, so far 

 as is known, undergo a complete segmentation. When hatched, the 

 young animal has the form of a Nauplius larva with three pairs 

 of appendages, of which the anterior (which become the anterior 

 antennre) are in the Estheridce only represented by slightly de- 

 veloped setigerous prominences. On the other hand, in Apus the 

 third pair is small and rudimentary. 



Almost all the Branckiopoda belong to inland waters, and prin- 

 cipally inhabit shallow fresh-water pools. When the latter dry up,, 

 the eggs, preserved in dry mud, remain capable of development. 

 Some species, as Artemia salina, are found in brine pools. 



Brancliipus pisciformis Schaff = B. stagnalis L., without a shell, found in 

 the lakes of Germany, together with Apus' cancriformis. B. diapJianws Pre>., 

 France. Artemia salina L., in salt pools, near Trieste. Montpellier. They 

 sometimes lay eggs with a hard shell, sometimes they are viviparous. Ajw* 

 cancriformis Schaff, with shield-shaped shell, Germany. The males, which are 

 rare, can be recognized by the normal formation of the eleventh pair of appen- 

 dages. They live in puddles and fresh- water lakes, together with Brancliipus. 

 Estlicria cycladoides Joly L., with perfect shell. 



Sub-order 2. Cladocera.* Water-fleas. Small laterally com- 



* Besides the- works already quoted, compare H. E. Strauss, "Memoire sur les 

 Daphina dc la classe des Crustaces," Mem. du Mus. d'Jiist nat., Tom V. and 



