^^"^ ZOOGENESIS ^'^ 



have a vast superiority over the protozoan, so far as concerns the 

 existence of the species the protozoan, because of the immense 

 number of individuals and their minute size, has an enormous 

 advantage over the crustacean or the fish. 



Biologically the protozoan, the fish and the crustacean are all 

 on an equal footing, in spite of the apparent arithmetical advan- 

 tage inherent in the multicellular structure of the body of the 

 crustacean and the fish. Indeed, whatever advantage there may 

 be rests with the protozoan, for very many different kinds of 

 protozoans live as commensals and as parasites within the bodies 

 of all fishes and crustaceans. 



There is another way of looking at the matter. The bodies of 

 all animals are at first composed of a single cell (figs . i lo, 1 1 1 , iii , 

 p. 185). In the case of the protozoan the body always remains a 

 single cell (fig. 87, p. 161), or at least special structures^ — which 

 may be very complicated — are formed without the division of the 

 cell as a whole. 



In the case of the multicellular animals the original germ cell 

 divides into two cells, these divide in the same way, and cell divi- 

 sion keeps on until the final form and complexity is attained (figs. 

 110-117; 111-1x5, p. 185). The division of the original germ cell 

 into two, however, adds nothing. The original potentiality of 

 the germ cell is simply enclosed in two packages instead of a 

 single one. Further cell division adds nothing. The original 

 potentialities of the germ cell are simply being segregated and 

 distributed in an increasingly large number of units. An adult 

 multicellular animal may therefore be considered as merely the 

 most effective form in which the fundamental attributes of the 

 original germ cell can find expression. 



It has been demonstrated by the study of genetics that muta- 

 tions are localized in the so-called chromosomes, which represent 

 a portion of the germ plasm, or contents of the germ cell. Thus 

 in the germ cell even minor variations in the characters or features 

 of any animal type are already present, although they will not be- 

 come evident until the germ cell has become divided up into thou- 

 sands or millions of cells. 



Any individual animal, therefore, no matter how complicated 

 its body may be, is simply the elaborated equivalent of its germ 

 cell. As such, it is the equivalent of a single celled animal or 

 protozoan. Assuming that a protozoan equals the number one, 



[2-37] 



