BRANCHIOPODA. 367 



characters of the appendages, the antennae and the others, 

 appear to remove them widely from the latter group and to 

 bear indisputable testimony to their Crustacean affinity. 



Order 2. BRANCHIOPODA.* 



Crustacea with an elongated and often distinctly segmented 

 body ; usually with a flat shield-like carapace or laterally com- 

 pressed bivalve shell, formed by a reduplicature of the skin. The 

 mandible is without a palp in the adult. There are at least four 

 and generally many pairs of swimming feet, which are in nearly 

 all cases leaf-like and lobed. 



The animals belonging to this order differ very considerably 

 in form and size, in the number of their segments and appendages, 

 as well as in their internal anatomy. They agree however in the 

 lobed and leaf-like character of their feet. Of the two groups 

 into which they are divided, the Phyllopoda are probably 

 the most primitive form of Crustacea which has survived. Their 

 primitive character is seen in the large and varying number of 

 segments of the body, the small degree of differentiation through- 

 out the series of their appendages, the tubular heart with the 

 segmentally arranged ostia, the simple character of the ganglionic 

 chain, and the persistence in all of them of the nauplius larva. 

 The other group, the Cladocera, may be regarded as an off-set 

 from this primitive stock (probably from a form allied to the 

 Conchostraca) in which the number of appendages and the size 

 of the body have been reduced and its segmentation obscured. 



The body is either cylindrical, elongated and clearly seg- 



* Besides the works of O. Fr. Miiller, Jurine, M. Edwards and Dana 

 compare Zaddach, De apodis cancriformis anatome et historia evolutionis, 

 Bonnae, 1841. E. Grube, Bemerkungen iiber die Phyllopoden, Arch, fur 

 Naturgeschichte, 1853 and 1855. Fr. Leydig, Monographic der Daph- 

 niden, Tubingen, 1860. C. Glaus, Zur Kenntniss d. Baues u. Entwick. v. 

 Branchipus u. Apus, Gottingen, 1873. Zur Kenntniss d. Organisation etc. 

 der Daphniden, Zeit. /. wiss. Zool. Bd. 27. Zur Kenntniss d. Baues u. d. 

 Organisation, der Polyphemiden, Denkschr. Akad Wien, Math. Nat. 

 Classe. Bd. 37, 1887. Branchipus and Artemia, Arb. Zool. Inst. Wien. vi. 

 A. Weismann, Naturgesch. d. Daphnoiden, Leipzig, 1876-79. Grobben, C., 

 Embryonalentwick. v. Moina rectirostris, Arb. Zool. Inst. Wien. ii. 

 Packard, Monog. N. Amer. Phyllopod Crustacea, Washington, 1883. P. 

 Samassa, Keimblatter-bildung bei Cladocera, Arch. f. mikr. Anal., Bd. 41. 

 G. O. Sars, Fauna Norvegiae, Vol. 1, Phyllocarida and Phyllopoda, 

 Christiania, 1896. M. T. Sudler, Devt. Penilia, Pr. 'Boston Soc. N. H., 

 Vol. 29, 1899, p. 109. Samter, Entw. Leptodora, Zeit. /. wiss. Zool. Bd. 

 68 (1900). Lilljeborg, Cladocera Suecica, NovaActa Soc. Sc. Upsala, 1900. 



