6 E. E. JUST. 



ence of the membrane, cleavage, and gastrulation. The naked 

 mass of endoplasm rounds up still attached to the developing egg. 

 It never reacts with sperm whether inseminated while attached to 

 the egg or after separated from the egg. Thus the presence of 

 the egg cortex is necessary for fertilization. Many observations 

 make this interpretation certain. 



In the egg of Arbacia the results are the same; indeed, if any- 

 thing, they are more clear-cut. 



Hypertonic sea-water is not the only agent that will bring about 

 this outflow of endoplasm. Frequently shaking will bring it about 

 in a few eggs of a given lot. Hypertonic sea-water is best, how- 

 ever, first because it produces a high per cent, of budded eggs, and 

 second because it makes very clear that the cortex is on the egg 

 and not on the endoplasmic mass. 



One additional method may be mentioned now because its use 

 has in turn led to some interesting experiments along another line. 

 This method involves the use of bolting silk, soft filter paper, and 

 lens paper. We may briefly consider this method. 



Uninseminated eggs of Echinarachnius are dropped on bolting 

 silk (in focus under low power of the microscope), the mesh of 

 which has a diameter less than that of the egg, stretched above the 

 surface of sea-water in a stender dish. If the concentration of 

 eggs in the drop of sea-water is just right, some eggs rupture as 

 they flow through the meshes of the silk. If the observer work 

 rapidly, he can after trial inseminate these eggs just as they burst. 

 The silk is then quickly thrust into the dish of sea-water. Some 

 of the eggs form membranes with naked buds attached. 



With filter paper the method is much the same. Soft moist 

 filter paper on which is placed a drop of eggs is mounted under the 

 microscope above sea-water in a low stender dish. The eggs flow 

 beneath the fibers of the filter paper and thus burst because of 

 pressure and slight drying. As they burst they are inseminated 

 and the paper plunged into sea-water. Some of these eggs later 

 show buds without membranes attached to cleaving eggs within 

 membranes. Intact eggs inseminated among the fibers of filter 

 paper in sea-water on insemination will develop normally. I have 

 kept such eggs through to the pluteus stage. With lens paper one 

 may obtain much the same results ; the lens paper, in addition, is 



