252 THE PRESENT IMPORTANCE OF SCIENCE 



economic values in a field originally explored without this 

 incentive. 



Briefly, the life-cycle of the mussel, as illustrated by 

 Figs. 28, 29, and 30, may be summarized as follows: The 

 sexes are separate, the spermatozoa are discharged freely 

 into the water, entering the body of the female with the 



I 



*sfc-#-<- 



m 



n 



FIG. 29. Glochidia of Lampsilis on Gill Filaments of a Fish. Above, small 

 portion of a filament with single glochidium partially overgrown thirty 

 minutes after original attachment. Below, small portion of a gill show- 

 ing several filaments heavily infected with glochidia, which are now 

 completely overgrown by the gill tissue. At moderate temperatures such 

 glochidia complete their parasitism in from three to four weeks. (After 

 Lefevre and Curtis.) 



respiratory water currents and there fertilizing the eggs 

 contained in brood-pouches which are formed by a modifica- 

 tion of the gills. Development now begins and continues 

 until a larval stage, known as the Glochidium, is reached. 

 In this state the young are discharged from the female. The 

 glochidium, which in size is near the limit of visibility for the 

 unaided eye, now rests upon the bottom and must perish 



