168 



INTRODUCTION TO ZOOLOGY. 



shadow of an approaching boat is thrown forward, so as to 

 cover them, they close the valves of their shells before any 

 undulation of the water can have reached them, thus showin"' 

 they are sensible to changes of light.* 



"The principal breeding season of the common oyster 

 {Fig. 159) is in April and May, when they cast forth their 



c m 



Fig. 159. — ANATOMY OP THE OYSTER.f 



young in little masses like drops of grease, formed of several 

 united together by an adhesive fluid, upon rocks, stones, or 

 other hard substances that happen to be near; and to these 

 the spats, as they are termed by fishermen, immediately 

 adhere, soon forming a thin shelly covering. Very commonly 

 they adhere to adult shells, and thus are formed the large 

 masses termed banks. Their growth is very rapid. In three 

 months they are larger than a shilling; and, at the end of the 

 first year, they have a diameter of two inches.''^ 



Shakspeare has said, " Honesty dwells like a miser in a 

 poor-house as your pearl in your foul oyster;" aud the con- 



* Owen, page 285. 



\ Fig. 159.— «, One of the valves of the shell — o', Hinge.— m, One of the lobes 

 of the mantle. — m', Portion of tlie other lobe folded back.— c, Adductor muscle. 



— ir, Branchia, or gills.— A, Mouth — t, Tentacula ■/, Liver.— i, Intestine.— a. 



Orifice.—/), heart. 



J Carpenter's Zoology, vol. ii. page 398. 



