724 NATURAL HISTORY OF AQUATIC ANIMALS. 



From these openings we will afterwards find, if the animal is sexually mature and the operation is 

 properly conducted, that the spawn will be forced out in a vermicular, creamy white stream. But 

 in order to fully expose the reproductive organ we should carefully continue to sever the mantle 

 of one side with a sharp penknife or small scissors, some distance forward of the great muscle 

 towards the head, cutting through the mantle just above the upper borders of the gills and following 

 a cavity which lies between the latter and the lower border of the visceral mass. A little 

 experience will teach one how far it is necessary to carry this incision of the mantle. For some 

 distance in front of the heart space the mantle is free or detached from the visceral mass and 

 reproductive organ which lies immediately beneath, and this enables one, if the last described 

 incision has been properly made, to almost completely expose the one side of the visceral mass 

 and the richly tinted, yellowish-white reproductive gland which constitutes its superficial portion. 

 The opening of the gland and its superficial ramifying ducts being laid bare on the exposed side 

 of the animal we are ready to press out the spawn on that side. Before beginning this, however, 

 it is important to observe that the principal duct passes down just along the edge of the visceral 

 mass where the latter bounds the heart space, in which the heart may be observed to slowly 

 pulsate, and that this great duct ends somewhere on the surface of the ventral blunted end of the 

 visceral mass. To expose the great or main generative duct it may be necessary to cut through 

 or remove the pericardial membrane which incloses or covers the heart space on the exposed side. 

 If the Oyster is sexually mature, the main duct will be observed to be distended with spawn, and 

 that, originating from it and branching out over almost the entire surface of the visceral mass, 

 there are minor ducts given off, which again and again subdivide. If these are noted, and it is 

 observed that they are engorged, giving them the appearance of a simple series of much branched 

 great veins filled with creamy white contents, it may be certainly presumed that your specimen is 

 mature and that spawn may be readily pressed from it. 



The operation of pressing the spawn out of the ducts requires care. The side of the end of the 

 pipette may be used, being careful not to crush or break open the ducts as you gently and firmly 

 stroke the pipette flatwise over the side of the visceral mass backward from the hinge towards 

 the heart space and over the great duct at the border of the latter diagonally downward and 

 backward to the opening of the reproductive organ. If this has been properly done it will be 

 found that the generative products are being pushed forward by the pipette through the ducts, 

 as the pressure will be seen to distend the latter, the contents of the branches flowing into the 

 larger and larger trunks until they are forced outward through the main duct and opening below 

 the great adductor, where they will pour out in a stream one-sixteenth of an inch or more in diameter 

 if the products are perfectly ripe. The sexes may be discriminated as described at the outset, and 

 it is well to first find a male by the method already given and proceed to express the milt as 

 described above into say a gUl of sea-water, adding pipetteful after pipetteful until it acquires a 

 milky or opalescent white color. As the milt or eggs are pressed out of the opening of the ducts 

 they are to be sucked up by the pipette and dropped into the water, the mixture of milt being first 

 prepared, to which the eggs may be added as they are expressed from the females. The judgment 

 of the operator is to be used in mixing the liquids; in practice I find that one male will supply 

 enough milt to fertilize the eggs obtained from three or four females, and it does not matter if the 

 operation takes from twenty to thirty minutes' time, as the male fluid, which it is best to prepare 

 first, will retain its vitality for that period. 



It is always desirable to be as careful as possible not to get fragments of other tissues mixed 

 with the eggs and milt, and the admixture of dirt of any kind is to be avoided. To separate 



