MICHIGAN ACADEMY OF SCIENCE. 



61 



the similarity of tliese plienoniena is, if anything, a proof of (he 

 extreme age and common origin of this process in all organisms 

 in which sexuality occurs. 



I will digress here for a moment and suggest that any system of 

 classification that disregards this ancient and common origin of 

 sexuality will eventually have to give way to a system in which 

 this is taken into consideration. I know that the currently ac- 

 cepted systems of classification as expressed by Engler and 

 Prantl by Lotsy or by Oltmanns are in direct opposition to these 

 views. The latter (and to a large extent the former) would derive 

 all algae from those groups of Flagellata in which there is no 

 sexual reproduction. These organisms are one-celled animals, some 

 possessing and some lacking chlorophyll, motile by means of two 

 flagella, and reproducing only by fission in the longitudinal direc- 

 tion. There are several groups which differ in the relative size 

 of the two flagella, in the color of the chloroplast, in the chemical 

 nature of the photosynthate, etc. Each of these is made by Olt- 

 manns and Lotsy the point of origin of a different algal series. 

 Thus the Heterocontae, the Teridineae and Acontae, the Phaeo- 

 phyceae, and the Volvocineae-Protococcales-Chaetophorales com- 

 plex all arise according to Lotsy from different, sexless Flagellate 

 groups. (Figure 1.) Within each of these series sexuality is as- 

 sumed to have arisen independently of the other groups. In so 

 far as the higher animals, the Metazoa, are derived possibly from 

 other groups of Flagellata the sexual process in these has still 

 a different origin. This seems to me to be all wrong and I predict 

 that the ideal phylogenetic classification of plants and animals 

 will change this entirely and indicate by its arrangement of the 

 groups of plants and animals the common origin of the sexual 

 process. 



What then are the essential features of sexual reproduction? 

 The most obvious phenomenon is the union of two cells to form 

 one (Fig. 2). In the most primitive organisms in which sexuality 

 is known (and by primitive we mean organisms that have appar- 



mt. 



Figure 2. Union of similar gametes of Hydrodictyon. (after Coulter) 



