PHYLLOPODA. BRAXCHIOPODA. 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 (Brcmchipus). 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 (Brcmchipus). 



The males are distinguished from the females principally by the 

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

 hooks (Estheridce), or by the modification of the posterior antenme 

 to form a prehensile apparatus (Brancliipus). Remarkable 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). The 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 

 antenna?) 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 Bra/nchiopoda 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. 



JBrancMpus jpisciformis Schaff = B. xtiujnuritt L.. without a shell, found iu 

 the lakes of Germany, together with Ajttis cdnrriformis. ]!. (tifijihanus Prev., 

 France. Artrmin x///i///i. L.. in salt pools, near Trieste, Montpellier. They 

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

 cancriforiiiix Schiiff. with shield-shaped shell. Germany. The males, which are 

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

 dages. They live in puddles and fresh-water lakes, together with Jirti/u'Jtijinx. 

 E.-itlu r'ia ay rind a! dcx .loly L.. with perfect shell. 



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



! Besides the works already quoted, compare H. K. Strauss. Memuire sur les 

 Dnphnia de la classe des Crnstaces," Mem. d>i M//x. </'}tixt nut.. Tom V. and 



