VITALITY 495 



interpret sex differences as originating through metabohc activities, 

 segregation of protoplasm thus differentiated, and distribution by 

 inequahties in division of the cell as Biitschli first suggested. 



Not only somatic differentiations with their specific functions, 

 but products of such differentiation in the form of gametes together 

 with the causes which bring about the attraction and fusion of 

 gametes, are all bound up in the ultimate significance of sex. Somatic 

 differentiations indicating male or female types are extremely rare 

 in Protozoa but problems of gamete formation and fusion are 

 presented by Protozoa of all kinds and so far as it applies to such 

 pro])lems, the term sex and its connotations apply to the unicellular 

 animals. 



There is little reason to doubt that a fundamental effect of sex 

 is the perpetuation of the species through union of gametes; and 

 there is equally little reason to doubt that the same function under- 

 lies conjugation and fertilization generally in Protozoa. It is 

 tacitly understood by biologists that the sum-total of conditions 

 leading to the production of eggs or of spermatozoa is typical of the 

 female or of the male, hence egg-like gametes in Protozoa are 

 regarded as the result of female activities, while spermatozoa-like 

 gametes come from males. This line of thought has led to the wide- 

 spread custom of describing macrogametes in Protozoa as female 

 and microgametes as male organisms. A difficulty has arisen 

 however, in connection with the entire absence of visible differences 

 between the gametes of many species distributed amongst all groups 

 of Protozoa, and here obviously, the attempt to apply any defini- 

 tion of sex fails completely. Yet such fertilizations are as fruitful 

 and as important for the species as are those in which gametic 

 diff'erences are well-marked. 



There are two fundamental biological problems associated with 

 the formation and fusion of gametes. These are : (1) The explanation 

 of the origin of gametic differences, and (2) explanation of the phe- 

 nomenon of attraction of gametes followed by their temporary or 

 permanent fusion. It would be mere presumption to claim that our 

 present state of knowledge permits an explanation of these phenom- 

 ena, but there is an abundance of data from which working hypothe- 

 ses may be deduced. 



Gametic Differences.— In Metazoa differences in gametes are 

 reduced to practically those between egg and spermatozoon. In 

 Protozoa there is no common t^pe of difference but all gradations 

 may be found here from apparently similar individuals to differ- 

 entiated eggs and spermatozoa. This has led to attempts to classify 

 gametes for purposes of description, into those which are similar 

 (isogametes) and those which are dissimilar (anisogametes). Similar 

 gametes, however, may be minute derivatives of adult individuals 

 —microgametes— or they may be adult individuals which cannot 



