200 THE PATH OF DEGENERATIVE EVOLUTION 



took place in a fluid. A special organ, the arche- 

 gonium, was developed ; this contained the ovum 

 and made the approach of the spermatozoa more 

 easy. 



For the present purpose we may omit considera- 

 tion of the mosses and liver- worts as it is improb- 

 able that they are in the line of ancestry of the 

 flowering plants. It is necessary only to say that 

 in them, while a single egg is produced in the 

 archegonium a large number of spermatozoa are 

 produced in the antheridium. 



The same condition is found among the fern-like 

 plants, but in their case, owing to the development 

 of special channels for the passage of nutritive 

 materials, it is possible for a much greater size to 

 be reached. In these circumstances it would be 

 unlikely that the spermatozoa should find at the 

 summit of a comparatively lofty plant the drop 

 of water necessary for the task of fertilization. 1 

 Accordingly the sexual cells are produced on 

 prothalli, which hardly reach above the surface of 

 the ground, and are in a favourable position for the 

 necessary moisture. 



In the less specialized ferns (fig. 70) a single 

 prothallus bears both male and female organs 

 (antheridia and archegonia). In the Equisetums 



1 The smaller forms like the Selaginellidae and the club-mosses 

 were represented in the past by plants of much greater size, as is 

 seen from fossil remains, and it is probable that the modern forms 

 have descended from these giants. 



