1884.] 141 [Hyatt 



The simplest free zoons of the Amoebinae may break by com- 

 plete agamic fission into many zoons, but this is evidently a prim- 

 itive unencysted condition introductory to the association in 

 simple colonies, which characterizes the adults of most of the 

 Protozoa, and to the more concentrated mode of reproduction by 

 complete fission within a cyst, which follows this stage in the 

 complicated cycles of transformation among the higher forms. 

 The Protozoon has normally three periods in its life, the youngest 

 individualized zoon, the intermediate or adult, during widen it 

 forms simple colonies, and the final reproductive encysted form, 

 which is an individualized zoon again. Ova and spermatocysts or 

 their homologues accompany the cysts in the higher Protozoa, and 

 are the direct descendants of the reproductive or encysted zoons. 

 They are the third products of the ontological cycle, and through 

 them all the influences of heredity are conveyed. By this per- 

 petual reduction of the cycle in every individual, and the con- 

 tinuous acquirement and transmission of new characteristics, 

 more and more complicated colonies appeared; and finally the 

 three-layered Metazoa were established. These have also the three 

 periods of life in homologous cells and in similar order, the indi- 

 vidualized zoons or cell of the ovum, the complex colony which is 

 built up by its growth and fission, and the production finally of 

 reproductive and encysted zoons or cells through which the in- 

 fluences of heredity are transmitted. These transformations, 

 however, occur in a very concentrated fashion, and the reproduc- 

 tive zoon must be considered as belonging to the young and 

 adult period of the complex colony instead of the degradation^ 

 or senile as in Protozoa. 1 



No connected colonies of zoons or cells are built up in the 

 Metazoa, representing the incompletely divided colonies of the 

 adults of Protozoa, except in incomplete segmentation of the 



1 We have formerly pointed out (Memoirs Bost, Soc. Nat. Hist., 1866, vol. 1; and 

 Proc. Amer. Assoc Adv. Soi., vol. xxxn, p. 354) that there was a constant tendency 

 among fossil Cephalopoda in the highest and most specialized forms (those which nec- 

 essarily possessed the most concentrated development.) to inherit senile characteristics 

 of progressive and earlier geological forms so that they appeared sometimes even in 

 larval periods. This law is of great interest since it enables us to correllate the trans- 

 formations of the senile individual with the degradations! changes taking place in the 

 highest and often most specialized forms occurring in the paracme of groups, and to 

 show that degradational transformations are similar in their results whether occurring 

 in the individual, or in the species, or in larger groups of the same class or branch. 



