Among plants one of the most important discoveries relates to these same reproductive elements, the spermatozoa, which by botanists are called antherozoids. A great difference between the whole higher series of plants, the flowering plants or phanerogams, and the cryptogams or lower plants, including ferns, mosses, and algae, was held to be that the latter produce vibratile spermatozoa like those of animals which swim in liquid and fertilise the motionless egg-cell of the plant. Two Japanese botanists (and the origin of this discovery from Japan, from the University of Tokio, in itself marks an era in the history of science), Hirase and Ikeno, astonished the botanical world fifteen years ago by showing that motile antherozoids or spermatozoa are produced by two gymnosperms, the ging-ko tree (or _Salisburya_) and the cycads (fig. 24). The pollen-tube, which is the fertilising agent in all other phanerogams, develops in these cone-bearing trees, beautiful motile spermatozoa, which swim in a cup of liquid provided for them in connection with the ovules. Thus a great distinction between phanerogams and cryptogams was broken down, and the actual nature of the pollen-tube as a potential parent of spermatozoids demonstrated. [Illustration: FIG. 24. Spermatozoa (antherozoids) of _Cycas revoluta_, seen from the side and from above. The spermatozoon is spherical, carrying a spiral band of minute vibratile hairs (_cilia_) by which it is propelled.] When we come to the results of the digging out and study of extinct plants and animals, the most remarkable results of all in regard to the affinities and pedigree of organisms have been obtained. Among plants the transition between cryptogams and phanerogams has been practically bridged over by the discovery that certain fern-like plants of the Coal Measures--the _Cycadofilices_, supposed to be true ferns, are really seed-bearing plants and not ferns at all, but phanerogams of a primitive type, allied to the cycads and gymnosperms. They have been re-christened _Pteridosperms_ by Scott, who, together with F. Oliver and Seward, has been the chief discoverer in this most interesting field. [Illustration: FIG. 25. The gigantic three-horned Reptile, _Triceratops_, as large as an Elephant, found in Jurassic strata in North America. A model of the skeleton may be seen in the Natural History Museum in London.] By their fossil remains whole series of new genera of extinct mammals have been traced through the tertiary strata of North America and their genetic connections established; and from yet older strata of the same prolific source we have almost complete knowledge of several genera of huge extinct _Dinosauria_ of great variety of form and habit (fig. 25). [Illustration: FIG. 26. Photograph of the skeleton of a large carnivorous Reptile from Triassic strata in North Russia, discovered by Professor Amalitzky and named by him, _Inostransevia_. The head alone is two feet in length.]