ACEPHALA OR LAMELLIBRANCHIATA. 



FIG. 632. FIG. 633. 



425 



J'/wlas Ha/.-tri, Desb. Reduced. 

 India. 



rimlas crixpata. Linn. 

 New Euglaud and eastward. 



FIG. 631. 



Boring Bivalves, Pliolas. 



producing 200,000 or 300,000 young in a season. The 

 eggs are hatched before they leave the parent ; and the 

 young of all species are very different from the parent, 

 and are swimmers, and have a pair of eyes in the normal 

 position. Bivalves grow rapidly, some kinds getting their 

 full growth in a single year. 



The nervous system consists of two pairs of sm;ilt 

 ganglia, one at the anterior and the other at the posterior 

 end, united by nervous cords or filaments. 



Naturalists generally recognize two great divisions of 

 the Acephals : 1. DIMYARIA (from the Gr. dis, two, and 



