350 Introduction to Animal Morphology . 



ter eggs, while in summer pseudova are produced by 

 parthenogenesis. 



Two orders are included : — 



I . Cladocera {Latreille) — including one family, short, com- 

 pressed, with a two-valved shell, which does not cover the 

 united large head and rudimental thorax. The front antennae 

 are small and palp-like, the second pair large, bristled, and 

 cleft, acting as oars and as claspers in the males. The eye 

 has often a ring of crystal cones around the central pigment 

 mass, and a secondary eye may be present beside it. The 

 unjointed post-abomen is bent down, with two claw-like 

 processes. The gill feet are four pair (Polyphemus, Evadne), 

 five (Daphnia, Lynceus), or six (Sida, Holopedium). In the 

 females the eggs are received into a brood-pouch between 

 the shell and the body posteriorly. Bosmina has two long 

 frontal processes covered with sensory rods. The larvae, on 

 emission from the egg, have the adult number of legs ; 20-50 

 pseudova are laid by each female, but only 1-3 winter eggs, 

 which are darker, with a compact yelk, and are surrounded 

 by a second shell or ephippium, derived from the lining of the 

 brood-pouch. 



Order 2. Phyllopoda {Latreille) — elongate, with often a 

 thin dorsal shell, but less perfect than in Cladocera ; eyes 

 two, large, and one or two small, stalked or sessile ; abdomen 

 many-jointed, tail-like posteriorly ; the thoracic limbs rudi- 

 mentary or none ; the abdominal leaf-like, except the first 

 pair ; mandibles without palps. Apus, Limnadia, and their 

 allies have sessile eyes, and a shield-like (Apus) or bivalved 

 mantle. Apus has two closely set eyes, two pair of rudimental 

 antennae, and sixty pair of branchiferous feet, of which the 

 first is the largest ; the eleventh has two rounded valve-like 

 flaps for holding the eggs, close to the sexual orifice ; the 

 seven hindmost abdominal joints have no limbs. Limnadia 

 has only 18-27 pair of legs. 



The stalked-eyed forms have no mantle, eleven pair of 

 gill feet, and a post-abdomen of 6-9 joints, with two movable 

 €nd-lamellas, at whose base the female has an egg-pouch, 

 most are marine, Branchipus and Chirocephalus are freshwater. 



