SEXUAL PHENOMENA IN THE PROTOZOA 213 



a renewed vitality, or in Butschli's words ('76) a renewal of youth 

 ( Verjiingung), expressed by increased activity in movements and 

 reproduction. Conjugation thus, as R. Hertwig insists, is not the 

 beginning of a series of reproductive acts, but occurs at or near the 

 end of such a series. Maupas's results seem to offer conclusive evi- 

 dence that the absence of conjugation involves a cumulative degener- 

 ative process which ultimately ends in death. The phenomena of 

 so-called sexual reproduction and of sex-differentiation have, in all 

 probability, grown out of this apparently fundamental requirement of 

 living protoplasm, namely, the periodic union of two cells ; and I 

 believe with Biitschli, Engelmann, Maupas, Hertwig, and many 

 others, that it cannot in itself be regarded as primarily a repro- 

 ductive act. None of the facts that have been determined show that 

 the morphological distinction of the sexes is a primary attribute or 

 property of living organisms, nor do any of the dynamic views of 

 fertilization afford an explanation of sex-differences any more than 

 does the statement of Geddes and Thompson cited above. Even 

 though the views of these authors be accepted, we should still have 

 to admit that no explanation of fertilization can be wholly satisfactory 

 unless it is equally applicable to forms which cannot be distinguished 

 as more anabolic or katabolic, i.e. to the conjugation of equal-sized 

 Infusoria, Mastigophora, or Sporozoa, as well as the union of differ- 

 entiated male and female cells. If then we define sex as the condi- 

 tion by which single-celled or many-celled organisms are differentiated 

 into male and female, we must admit that the origin of sex is only a 

 part of the problem, for fertilization occurs between individuals in 

 which there is no apparent sex-difference, as well as between those 

 possessing it. 



In the present chapter I have brought together some of the evi- 

 dence which bears upon these several points. A number of phe- 

 nomena which accompany reproduction in the higher animals, and 

 which have attracted so much attention among biologists of all times, 

 are seen in simpler forms in Protozoa. Among these the phenomena 

 of sex-differentiation, of maturation or preparation for fertilization, 

 and fertilization itself are of paramount interest. 



The explanation of sex-differentiation is not as yet made more 

 easy by the study of Protozoa, and here as in higher animals it must 

 remain entirely hypothetical until future research throws more light 

 upon the problem. The conditions accompanying conjugation, how- 

 ever, have been carefully studied and analyzed in relation to other 

 vital functions of the cell, and the evidence thus acquired gives a clue, 

 I believe, to an ultimate explanation of fertilization. An important 

 underlying principle was first made out by Biitschli {'j6) and Engel- 

 mann ('76) upon degenerating Infusoria, and was expressed by Minot 



