442 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



MATURATION AND FERTILIZATION. 



Because of the opacity of the egg, satisfactory observations on the 

 phenomena of maturation and fertilization are impossible during life, 

 except for those changes which take place on the outside. A few 

 minutes after the egg is laid the first polar body is given off at the 

 upper pole of the egg. The second polar globule follows after a very 

 short interval. These structures are of an ephemeral nature and soon 

 disintegrate or pass out into the water and are lost. Nothing can be 

 made out of their internal structure or of the arrangement of the 

 chromatin with the low magnification which one is obliged to use in 

 the study of the living egg. However, I was fortunate enough to get 

 sections of the early stages of preserved eggs which show the polar 

 bodies in the process of being extruded. The germinal vesicle moves 

 to the periphery of the egg, then a part of its substance is divided off 

 and extruded as the first polar body. In plate 32, figure 16, which is a 

 section of an egg that was preserved a few minutes after it had been 

 laid, the second polar body is just being given off. It contains several 

 granules of chromatin scattered through its clear hyaline substance. 

 In the first polar body, which has moved a little distance from the 

 egg, but is still held in connection with it by some means of attachment, 

 the chromatin has come together and forms a single mass in the center 

 of the polar globule. The means of attachment of the polar bodies 

 to the surface of the egg is not quite clear, as the egg is destitute of a 

 membrane. It is possible that some of the clear liquid part of the 

 protoplasm may exude from the substance of the egg as the polar 

 bodies are extruded, and be the means of holding them to the surface 

 of the egg even during fixation. 



As can be seen in the figure, the germinal vesicle during the extrusion 

 of the polar bodies is situated at the very edge of the egg; about half 

 of its bulk even extends beyond the general contour of the surface. 

 The yolk granules are crowded around the nucleus with the same 

 density as in other parts of the egg. After the second polar body has 

 been given off, the female pronucleus moves back from the periphery 

 some distance. Here it is met by the sperm nucleus and fusion of the 

 two takes place. Whether there is any definite spot for the entrance 

 of the spermatozoon or not, could not be decided. But I am inclined 

 to think that the sperm is capable of penetrating the egg at any part; 



