128 THE EVOLUTION OF SEX. 



The student will already see the relative femaleness of the large units, the 

 maleness of their smaller neighbours. 



(3.) A third stage is reached in another alga, Ectocarpiis, which is 

 peculiarly instructive. This may separate off large cells which develop by 

 themselves like parthenogenetic ova. From other parts of the plant 

 smaller units are liberated, which generally, though not yet invariably, 

 unite with one another before developing. But between these smaller units 

 a most important physiological difference has been observed by Berthold. 

 Some soon come to rest and settle dnwn, and with these their more 

 energetic neighbours by-and-by unite. We have here a very distinct 

 beginning of the distinction between male and female elements. The 

 comparatively sluggish, more nutritive, preponderatingly anabolic cells, 

 which soon settle down — are female ; the more mobile, finally more 

 exhausted and emphatically katabolic cells — are male. As Vines says, 

 " the one is passive, the other active ; the former is to be regarded as the 

 female, and the latter as the male reproductive cell." 



(4.) Further, in another alga, Ciitleria, the differentiation may be 

 traced. Two kinds of units result, which must unite with one another if 

 development is to take place, but these units arise from perfectly distinct 

 sources in the parent plant. The larger less mobile cells, which soon come 

 to rest, are fertilised by the smaller more active units. The more anabolic 

 or female cells are fertilised by the more katabolic or male cells, which 

 have now gone too far for the possibility of independent development. 



(5.) To complete the series, we may simply mention such a case as that 

 to which we shall presently return, — those forms of Volvox, where an 

 entire colony of cells produces either female or male elements, thus repre- 

 senting the beginning of an entirely unisexual many-celled organism. 



While the above cases also involve the problem of the 

 origin of fertilisation, which is left over for the present, they 

 confirm most clearly our general conclusion that preponderant 

 katabolism or anabolism are the ruling characteristics of male 

 or female respectively. 



i:^. 5. Nature of Sex as seen in Origin among Animals. — 

 Among the Protozoa also, we can trace the beginnings of the 

 same "dimorphism" between male and female. A union 

 between similar cells is of course frequent, but that is not at 

 present to the point. What we refer to, are the numerous cases, 

 especially among flagellate and vorticella-like infusorians, 

 where the two individuals which unite are quite unlike one 

 another both in form and history. " There can be no doubt," 

 Hatchett Jackson remarks, " that the process is essentially a 

 sexual one ; when the individuals are invariably different, there 

 is no reason why the terms male and female should not be 

 applied to them." In some cases we find as before that a small 

 active katabolic unit combines with a larger, more passive, 

 and anabolic individual. 



