54 FISH—CULTURAL ASSOCIATION. 
ward cleaning the ova from the minute fragments of tissue be- 
fore allowing development to go on. Another method which I 
have employed, and one which is even better than this, is to 
clear the animal from all flesh, such as gills, mantle aud muscle, 
by cutting off the parts with a pair of small scissors, then taking 
the body between the fingers, place the outlet of the generative 
organs against the side of the small vessel or plate, and with a 
flat instrument of some kind, such as a dull knife, gradually 
manipulate the sides of the organ, and press the products down 
and out into the dish. In this manner, if the specimen is ripe, 
you will have a clear milky liquid, with none or only a very 
slight admixture of foreign material. The mixing of the male 
and female elements can then be performed as already explained. 
After thoroughly cleansing the ova they were left quiet for some 
considerable time, and in from two to four or six hours a layer 
of embryo could be seen at the surface of the water, each indi- 
vidual moving about in a very brisk ‘‘go-as-you-please” sort of 
fashion. These were then siphoned off into a larger vessel, and 
after several layers had been disposed of, the assembly was placed 
in the breeding-jar, and the water set in motion through their 
new locality. In the case of the experiment begun on the 25th 
of July and above mentioned, specimens were examined every 
few hours in order to denote the development, and during one 
such examination on the 17th inst., about forty-four hours after 
the ova had been impregnated, one of the young oysters, which 
had developed so far as to be entirely enclosed by its two shells 
within the field of the microscope, thrust out a portion of the 
velum and firmly secured itself to the glass slide upon which it 
had been placed. Further observation seems to show that this 
is their normal mode of attachment, that is, to thrust out the 
velum from between the shells and adhere to whatever is within 
reach, afterward the animal falls over to one side, generally the 
left, and the shell of that side gradually forms around and out 
beyond this attachment of the young animal. Later a portion 
of shell material forms under the attachment and firmly solid- 
ifies the shell proper to the attached substance, and the fleshy 
attachment atrophies, so that while at first the animal itself is 
attached to the outer world, later in life the shell is the part at- 
