300 PHYLUM ARTHROPODA. 
6. First thoracic foot (leg-like). 
7-16. Other ten thoracic feet (swimmers). 
The 16th in the female carries an egg-sac or brood- 
chamber. There are eleven thoracic rings on the body. 
Abdominal 17-68. Fifty-two abdominal feet, to which there corre- 
(Post-genital). | spond only seventeen rings on the body. 
The large dorsal shield is not attached to the segments behind the 
one bearing the maxillipedes. Many of the thin limbs doubtless 
function as gills. The genital apertures are on the sixteenth 
appendages. The anus is on the last segment of the body. 
Thoracic 
(Pregenital). 
Fic. 154.—Daphnia, 
£., Eye; A.®, second antenna; A.1, first antenna; de., digestive cxca; SLs; 
shell gland; go., gonad; 4., heart in. pericardium ; o., ovum; L.p., 
brood-pouch; sf., spine; /, furca; s., setae; Aé., rudimentary abdomen ; 
z., caudal fork; g., gut; 745, thoracic limbs. 
There is a pair of ventral ganglia to each pair of limbs; the ventral 
nerve-cords are widely apart; and the cephalic ganglion is 
remarkably isolated. There is periodic parthenogenesis. 
