10 



dark green digestive glaud. Back of the stomach the smaii, 

 convoluted intestine may be seen, cut at several points by the 

 section, 



REPRODUCTION AND DEVELOPMENT. 



In the common, or Eastern, oyster the sexes are separate, 

 each individual being either male or female, but not both, as 

 iy the case with the European oyster, and in one of the species 

 found on the Pacific Coast. It has been maintained by some 

 observers, but the point is not yet definitely proven, that the 

 same individual may vary in sex from year to year, producing 

 eggs at one breeding season and sperm at the next. 



While the sexes vary much in physiology, and in their 

 histological structure, it is impossible to distinguish between 

 the males and females by any known external characters. It is 

 only by a careful examination of the reproductive glands, or bet- 

 ter of the sexual products, that one sex may be distinguished 

 from the other. 



The simplest method for determining the sex of an oyster 

 IS to examine a drop of the genital products, which may be 

 obtained by cutting into the reproductive organs on either side 

 of the body mass. If the drop is put on a piece of clear glass 

 and examined without any magnification, it will be seen that, 

 if taken from a female, the reproductive elements will have a 

 slightly granular appearance. In those taken from a male no 

 separate particles can be made out; but the Avhole mass will 

 have a slightly quivering appearance due to the cnmbinod move- 

 n (-.1^; of the spermatozoa. 



RIPENING OF THE GENERATIVE ORGANS. 



In the sin'ino-. when the water begins to become warm, cer- 

 tain -.'hanges manifest themselves in the generative oroans of 

 the oysters preparatory to the act of spawning. In the female 

 some of the minute eggs in the ovary increase in size and become 

 loosened from the follicles, or little pockets of tissue, in which 

 they have undergone their early development. All of the egga 

 which are to be discharged at one season do not ripen at the same 

 time so that the spaivning of each individual extends over a 

 greater or less period of time. An examination of the ovary 



