CEDOGONIUM. 89 



have been evolved ; but in Volvox the insertion of the cilia has under- 

 gone a lateral displacement, so that they now spring from the base of 

 the mouth-piece. 



The large egg-cells, although not escaping from the mother colony 

 into the surrounding water before fecundation, are in a measure free 

 to move passively within the mother colony. The same kind of 

 stimulus operative in bringing the eggs and spermatozoids together in 

 tttcus may in all probability obtain also in Volvox. In the case of 

 dioecious forms especially, investigation along this line will probably 

 yield important results, and with modern technique a careful study of 

 the behavior of the sexual nuclei and other cytological details of fecun- 

 dation, concerning which we know practically nothing, will also bring 

 to light much of value and interest to our knowledge of fecundation. 



CEDOGONIUM. 



We shall now pass to the consideration of the sexual process in 

 certain of those fresh-water algae in which the female gamete remains 

 enclosed in its more specialized and characteristic organ, the oogonium. 



Beginning with such forms as Cylindrocapsa and CEdogonium we 

 have a progressive series of forms culminating in Coleochcete, in which, 

 apart from the specialized bisexual products, there are more highly 

 differentiated and characteristic sexual organs. 



The nature and development of the sexual organs in CEdogonium 

 and the process of fecundation have been carefully described by Pring- 

 sheim ('56) and others in so far as these phenomena may be followed 

 with accuracy in the living material, but, as regards the more minute 

 structure of the spermatozoid and egg-cell and the behavior of the 

 sexual nuclei in fecundation, the researches of earlier observers leave 

 much to be desired. In more recent years Klebahn ('91) has suc- 

 ceeded in filling in many of the gaps, and it is to his investigations 

 that we are chiefly indebted for a more detailed knowledge of the 

 behavior of the nuclei. 



When the oogonium (CEdogonium boscii) has attained its defini- 

 tive form, the protoplasm, which encloses a large vacuole, is every- 

 where closely applied to the cell-wall. Changes which lead to the 

 formation of the opening in the upper part of the organ are then 

 manifested. Near the spot at which the oogonium will open a small 

 elliptical lamella is formed, which gives a cellulose reaction. The 

 formation of the lamella proceeds from a colorless portion of the cyto- 

 plasm, which can not be distinguished at an earlier stage. Between 

 cell-wall and lamella a lens-shaped cavity arises, and a transverse slit 



