198 



GENERAL ZOOLOGY 



Development. In the months of May to September, in 

 the latitude of Baltimore, the male and female oysters send 

 out into the water their spermatozoa and their eggs. A 

 female oyster may yield in one season at least sixteen mil- 

 lion and probably as many as sixty million eggs. The num- 

 ber of male cells is great beyond all powers of expression. 

 Of course we should expect that in spite of the countless 

 spermatozoa, many eggs would never be fertilized at all, 



on account of their being carried 

 away by unfavorable currents. 

 Eggs that are not carried away 

 fall to the bottom naturally. 

 Those eggs which are fertilized 

 swim to the surface as larvae 

 after a few hours' development. 

 There surface fish may, as Pro- 

 fessor William K. Brooks once 

 suggested, "gulp down in a few 

 seconds oysters equal in number 

 to the population of Baltimore. " 

 Within one to six days after 

 fertilization the oyster "fry" 

 (swimming larvae, Fig. 105) sink to the bottom again and 

 affix themselves to whatever solid object they happen to 

 touch. At this time they are about three tenths of a mil- 

 limeter (one eightieth of an inch) long. For a few weeks 

 after beginning their stationary life they are liable to be 

 crunched to death by voracious crabs, — among others, the 

 blue crab (Fig. 87). 



Economic Importance. The largest and most important 

 "oyster farms" along our coast are in Chesapeake Bay. 

 There and elsewhere the beds have been surveyed and leased 

 under laws of the states. So vast is the oyster-fishing indus- 

 try in this country that more than fourteen millions of dol- 



Fig. 105. Oyster larva. 

 (Much enlarged) 



1, mouth; 2, stomach; 3, anus; 



U, shell; 5, adductor muscle; 6, 



circle of cilia. (After Moebius) 



