124 THE EVOLUTION OF SEX. 



degree of accuracy, under the metaphor of an eddy in a stream, 

 or of a ceaseless fountain, which, while remaining approximately 

 constant, is the expression of continual ascent and descent of 

 drops. The protoplasm itself must often be in as ceaseless 

 change as the apex of the jet. 



In active, motile, ciliated, or flagellate cells, whether they be 

 constant forms or only temporary phases, there is predominant 

 katabolism, — predominant when compared with the life expen- 

 diture of a passive, quiescent, enclosed, or encysted cell. In 

 amoeboid organisms these extremes are avoided ; there is cer- 

 tainly great amplitude of variation still, but neither anabolism 

 nor katabolism gains the ascendant in any marked degree. 



Suppose, then, in such an amoeboid cell, a continued 

 surplus of anabolism over katabolism, the result is necessarily 

 a gro\vth in size, a reduction of kinetic energy and movement, 

 an increase in potential energy and reserve food-material. 

 Irregularities ^^■ill tend to disappear, surface-tension too may 

 aid, and the cell acquires a spheroidal form. The result — 

 surely intelligible enough — is a large and quiescent ovTim. 



It will be remembered that young ova are very frequently 

 amceboid ; that with a copious nutrition this disappears in 

 varying degrees of encystment; that ensheathing envelopes 

 arising from the ovum, sweated off like cysts round Protozoa, 

 are exceedingly common ; and that ova are the largest of all 

 animal cells. 



Starting once more from an amceboid cell, if katabolism 

 comes to be more and more predominant, the increasing libera- 

 tion of kinetic energy thus implied must find its outward 

 expression in increased activity of movement and in diminished 

 size ; the more active cell becomes modified in form, in adapta- 

 tion to passage through its fluid environment, and the natural 

 result is a flagellate sperm. 



In short, then, the respective morphological characters of the 

 sex-cells, female and male, find the same physiological rationale as 

 do the large passive encysted and smaller active ciliated phases 

 of the cell-cycle in general, and are alike the outcome and 

 expression of predominant anabolism and katabolism respec- 

 tively. Here again we reach the same formula as before ; or, 

 more cumbrously in words — the functions are either self-main- 

 taining or species maintaining, individual or reproductive ; the 

 former are divided into anabolic and katabolic, the latter into 

 male and female. But the second set of products and processes, 



