648 
T. H. MORGAN 
disc, and yet excite in it those changes that would lead to its 
development. In such a process the embryo would be purely 
maternal — owing only to the male its impulse to begin its develop- 
ment, but none of its material. The evidence of many sections 
goes to show, however, that the spermatozoa are carried into the 
blastodisc, and that one at least unites with the egg nucleus as in 
normal fertilization. 
The method by which the protoplasm is drawn into the blastodisc 
It has long been known to students of fish development that 
after deposition there is a steady movement of the peripheral 
protoplasm of the egg into the blastodisc. The cause of this 
movement is entirely unknown and seldom discussed. It is not, 
however, a unique phenomenon, for something like it seems to 
occur in other eggs, although not alwaj's in the same direction, or 
under the same conditions. Conklin has given some very full 
and accurate descriptions of such movements in the eggs of several 
gasteropods. In some of these the movement seems to be con- 
nected with the dissolution of the germinal vesicle in consequence 
of which the protoplasm becomes more fluid. In the ascidians 
the movements are connected with the entrance of the spermato- 
zoon. In the fish the latter event cannot be the cause of the move- 
ment, since it takes place in the unfertilized egg; and it is improb- 
able that the dissolution of the nucleus is its chief cause since the 
movement goes on throughout the entire time of polar body for- 
mation and conjugation of the pronuclei, and even during the 
early cleavages. The concentration is not connected with the 
absorption of water b}^ the egg to make the protoplasm more 
liquid and no swelling of the membrane to set free the interior 
takes place as measurements, that I made, show. The surface 
of the egg is under high pressure as seen by sticking the egg, 
when the yolk rushes out through the opening. The enveloping 
protoplasm shrinks, but the membrane remains as before. By 
flattening the egg between glass plates the yolk often breaks 
inside the membrane through the surface layer of protoplasm 
of the egg, and escapes into the space between the membrane 
