A. Hyatt — Larval Theory of the Origin of Tissue. 333 

 in place of loosely connected colonies as among Proto- 



* 



zoa. 



The many disconnected, wandering cells with their inde 

 pendent organization, and functions favor 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 amoebae, and it has been assumed that 

 these cells are the equivalents of the adult amoebae. 



Morphologically this seems to be true, but it does not ac- 

 count for the physiological differences between the Protozoon 

 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 re- 

 production 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 Amoebae, 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 characteristics while 

 losing their later acquired flagellate and ciliate similarities. 



We cannot use the words embryo and larva, which belong to 

 the ovum after impregnation, and we, therefore, propose to des- 

 ignate the cell an autotemnon,f in contrast with the embryo, 

 which is more specialized. The least specialized tissue cells of 



* The net work of protoplasm connecting tissue cells is disregarded in order 

 to show the massive nature of tissues and at the same time state their character- 

 istic cellular composition. 



f From Avtoq, self, and rifivu, to divide. 



