THE EVOLUTION OF SEX 35 



the ovum. In the flowerless plants, such as 

 ferns and mosses, there are actively locomotor 

 spermatozoa or antherozooids (see Fig. 6), but 

 though there long seemed to be no inter- 

 mediate step between this and the seeming 



FIG. 5. Ovum and spermatozoon (S) of a sea-urchin, alike- 

 magnified over 760 times, showing relative size. (After 

 E. B. Wilson.) The ovum shows the cell-substance or 

 cytoplasm (C) with an intricate structure, the nucleus (N) 

 with readily stainable bodies known as chromatin threads 

 (CHR), and with a nucleolus or germinal spot (GS). 



static pollen grain of higher plants, a mobile 

 spermatozoon has been found to emerge from 

 the pollen tube in certain cycads, and also 

 in the strange Gingko or Maiden-hair Tree 

 brought to our gardens from the temple 

 enclosures of old Japan. And the pollen- 



