Hyatt.] 396 [Nov. 16, 



General Meeting, Nov. 16, 1887. 



Prof. W. H. Niles in the chair. 

 The following paper was read : 



VALUES IN CLASSIFICATION OF THE STAGES OF 



GROWTH AND DECLINE, WITH PROPOSITIONS 



FOR A NEW NOMENCLATURE. 



BY ALPHEUS HYATT. 



In accord with views brought to the notice of the society in 1884, 

 under the title of the "Larval Theory of the Origin of Tissue," 1 

 an abstract of which was subsequently printed in Amer. Journ. 

 Sci., May 31, 1886, we divide the animal kingdom into three com- 

 prehensive divisions: (1) Protozoa, unicellular animals, which 

 propagate by means of asexual (autotemnic) fission and by spores, 

 and build up colonies, but always remain typically unicellular. 

 (2) Mesozoa, multicellular colonies, but composed of only one 

 layer of cells, so closely connected, that they may be called a prim- 

 itive tissue, and having more or less spherical forms. 2 They prop- 

 agate by means of ova, spermatozoa, and by autotemnic fission, 3 

 and have an aula or common cavity, but no specialized digestive 

 cavity or archenteron. (3) Metazoa, complexes of multicellular 

 colonies, in which growth by sexual union, and resulting fission 

 of the ovum, forms three primitive tissue layers and builds up a 

 body in which an archenteron is always developed. They propa- 

 gate always by means of ova and spermatozoa, autotemnic fission 

 occurring only, if at all, during the earliest stages of the ovum. 

 Holoblastic ova may be regarded as the more primitive or gener- 

 alized forms to which all other forms of ova having more or less 



1 Proc. Bost. Soc. Nat. Hist., xxill, 1884, p. 45. 



2 See Butschli's remark that the closely appressed hexagonal cells of the envelope 

 are connected with each other by threads of protoplasm. Bronn. Thierreichs, I, 

 Protoz., p. 775. 



3 The best summary of all observations is in the work just quoted, where Biitschli 

 calls the sexual cells ova and spermatophora, but alludes to the cells developing by au- 

 totemnic fission as Parthenogonidia. They are by his own descriptions and those of 

 others, ova, which differ from sexualized ova only in their ability to develop through 

 autotemnic fission. 



