PHYLOGENY. 79 



riod, the greatest known development of the Pterido- 

 phyta (Lycopodia, ferns, Equiseta) took place, while 

 the Gymnosperms were still represented by a few gen- 

 era. Their period of development or acme arrived in 

 the Mesozoic ages, and the Pteridophyta underwent a 

 corresponding reduction of numbers and importance. 

 Not until the upper Cretaceous epoch did the Angio- 

 spermous Phanerogams with their attractive flowers 

 appear, and from that period to the present they have 

 gained and maintained the ascendency. In accord- 

 ance with the mode of origin of tubular flowers by the 

 fusion of the separate petals of polypetalous forms, 

 we find that the former succeeded the latter in time. 



We may review this brief sketch of the paleontol- 

 ogy of plants in the preceding phylogenetic table. 



Turning now to the animal kingdom, its order of 

 succession may also be perceived in existing species. 

 As with plants we commence with unicellular asexual 

 forms (Protozoa). Some of these increase by division 

 only (Rhizopoda), while others must occasionally con- 

 jugate, since, according to Maupas, the reproductive 

 energy is exhausted by continued self-division (Infuso- 

 ria). Such structural specializations as the highest of 

 the Protozoa possess, are merely vacuities or processes 

 of their material, for the purpose of internal or exter- 

 nal motion. In the second grade of organization ani- 

 mals are multicellular, or composed of more than one 

 protoplasmic unit. The simplest of these, as Volvox, 

 contains no specialized organs, but seems like a colony 

 of Protozoa, although all its cells are not exactly alike 

 (Ryder). An appreciable advance of structure de- 

 fines the next class, the Coslenterata. Here the mul- 

 ticellular mass contains a distinct digestive chamber, 

 from which usually radiate tubes towards the periph- 



