Origin of Sex. 303 



division takes place. According to Haeckel the Protomyxa, one of the 

 slime moulds (myxomycetes) passes through three or four stages of de- 

 velopment. First, it is seen as a mass of slimy protoplasm ; then it be- 



FIG. 128. 



FIG. 128. Metamorphoses of the slime mould Protomyxa. (After Hseckel.) 



a. Protomyxa encysted. 



6. Division of the protoplasm into individuals within the cyst, 

 c. Bursting of the cyst and liberation of the tailed spores. 

 d. Transformation of the spores into amoebae, which unite to form the plasmodium. 



comes a little ball enclosed in a bladder or cyst, and it is then said to 

 be encysted. The protoplasm inside the cyst becomes separated into a 

 number of nuclei, each of which develops into active spores with tails. 

 When this development is complete the wall of the cyst becomes rup- 

 tured and the spores escape. In a short time these tailed spores become 

 so many amoebae ; and finally a lot of these amoebae join together to form 

 a slimy amoeboid mass called a plasmodium. The fusion of these pro- 

 toplastic units in the formation of this new body illustrates the union 

 of the sexual elements, if it is not itself a primitive example of such 

 union. These units, before the bursting of the cyst, appear to be un- 

 der an influence that causes them to repel each other. After their liber- 

 ation they are subjected to an opposite influence and they attract. Such 

 attraction continues to draw these elements together until a new cyst 

 is formed, when the force is reversed and the operation is repeated. 

 The essential elements of sex, then, taking this case as an illustration, 

 consist of two cells of equivalent value, which are first consolidated by 

 the predominant energy of their environment into a new body, which 

 then falls under influences that cause its segmentation into cells in the 



