214 



BIOLOGICAL LECTURES. 



sea-water, the normal mitotic activity is immediately resumed. 

 The maturation processes, including the extrusion of the first 

 and second polar globules and the concomitant changes in the 

 form of the egg, succeed one another with the same regularity 

 that obtains when the Qgg is fertilized. In both instances the 

 Q.g^, at first spherical, becomes flattened at the animal pole 

 just before the first polar globule is formed, but soon regains 



Fig. 6. — Diagram showing some of tlie changes in the form of the oocyte and egg-cell which 

 take place upon the entrance of the spermatozoon or upon the addition of potassium 

 chloride to the sea-water. A , primary oocyte before the first polar globule is formed ; 

 ' B, secondary oocyte flattened at the animal pole, first polar globule ; C, shape assumed 

 when the second polar globule is formed ; D, formation of the yolk-lobe. (These form- 

 changes are not so pronounced in eggs taken from animals which have been removed 

 from their tubes and have been kept for a few days in an aquarium.) 



its original form. About the time the second polar globule is 

 formed, the contour again changes and the tg^ becomes pear- 

 shaped, the apex towards the animal pole. After this the egg 

 again assumes the form of a sphere (Fig. 6), 



But the similarity between the behavior of the fertilized eggs 

 and those subjected to potassium chloride does not stop here, 

 for the " yolk-lobe," a protuberance at the vegetative pole, is 

 formed in both in essentially the same manner. In the ferti- 

 lized Q.ggy however, the first cleavage-furrow cuts the ^gg into 



