194 Mr. A. Hyatt 07i the 



and the rapidity of the processes of complete fission, due to 

 concentration, produces masses of tissue and membranes in 

 place of loosely connected colonies, as among Protozoa*. 



The many disconnected wandering cells, with their inde- 

 pendent organization and functions, favour this conclusion, and 

 the sight of these and of ova in the mesenchyme of sponges, 

 and the evidence of their functions here and elsewhere in the 

 animal kingdom, is sufficient to bring a candid mind to open 

 confession of the existence of exact parallelism between them 

 and the single individualized Amoeba. 



These and other morphological facts have led, so far as we 

 know, only to comparisons between the ordinary tissue-cells 

 and the adults of the Amoebaj, and it has been assumed that 

 these cells are the equivalents of the adult Amoebse. 



Morphologically this seems to be true ; but it does not 

 account for the physiological differences between the Proto- 

 zoon and the cell. The ontology of the cell, its production 

 of tissue, and the reduction of the cycle of transformations 

 cannot be explained unless we attribute to it a concentrated 

 energy in reproduction and a tendency to form closely 

 united and complex associations much greater than that of the 

 Protozoon. 



Thus a single Metazoon is a colony of infinite complexity 

 in which the two primitive colonies, ectoderm and endoderm, 

 have produced by growth and agamic fission all the anatomical 

 systems and their various organs and smaller parts. 



Studies of reproduction show that the succession of events 

 among Protozoa was first growth, then fission, then the union 

 or concrescence of divided zoons and an exchange of their 

 complementary parts ; evidently all of these influences bear 

 upon the tissue-cell and influence its reproduction. Never- 

 theless two cells do not combine previous to reproduction by 

 fission, and whatever the effect of the original impregnation 

 may be, we are obliged therefore to regard a young cell as a 

 modified agamic larva-like form or zoon when compared 

 with the full-grown Amoeba. If descent from Amcebse 

 through Flagellata and Ciliata is assumed, then the task of 

 proving young cells to be immature forms becomes easier. 

 In this case they are obviously forms which, like the ova of 

 many Metazoa, have retained their ancient amoeboidal charac- 

 teristics, while losing their later-acquired flagellate and 

 ciliate similarities. 



We cannot use the words embryo and larva, which belong 



* The network of protoplasm connecting tissue-cells is disregarded in 

 order to sliow the massive nature of tissues and at the same time state 

 their characteristic cellular composition. 



