MOLLUSCA. 



417 



so rapid, that in three days after the deposition of the 

 spawn, the shell of the young oyster is nearly a quarter of 

 an inch broad; in three months it is larger than a shilling. 

 The spawn is a very interesting object for microscopic exa- 

 mination, especially with polarised light. The young fry is 

 represented in fig. 214 ; some have their cilia protruded. 



In the stomach of the Oyster, and in the alimentary 

 canal, myriads of living Monads and other Infusoria are 

 found swimming about in great activity, and swarms of a 

 conglomerate and ciliated living organism, which somewhat 

 resemble the Volvox globator, but so extremely delicate in 



Fig. 208. 



1, A transverse section of a Pearl from Oyster, showing its prismatic structure. 

 2, A transverse section of another Pearl, showing its central cellular structure, 

 with outside rings of true pearly matter. (Magnified 50 diameters.) 



their structure, that they require a slight charring to be 

 rendered permanently visible. 

 E E 



