300 



PHYLUM ARTHROPODA. 



(6. First thoracic foot (leg-like). 

 7-16. Other ten thoracic feet (swimmers) 

 The 1 6th in the female carries an egg -sac or brood- 

 chamber. There are eleven thoracic rings on the body. 

 Abdominal f 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. 



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. 



