HARDWICKE'S SCIENCE-GOSSIP. 



pass away, leaving only small and humble represen- 

 tatives, and the great reign of reptiles sets in, reptiles 

 which exceeded in size any other animal before or 

 since ; carnivorous reptiles, flying reptiles, and reptiles 

 which by almost imperceptible transitions became the 

 ancestors of birds. These uncanny, hot and fier)' 

 times seem to have suited these cold-blooded creatures, 

 but the puzzle remains why they|should have died out 

 whilst climatic conditions remained to all appearance 

 the same. Mammals too first become known to us 

 in this age ; feeble creatures giving little promise of 

 future greatness, but even in the Jurassic age with 

 jaws and teeth sharply differentiated into the placental 

 and implacental types of dentition. No such appal- 

 ling break occurs in the world of plants, where tran- 

 sitional forms abound at every stage. We have no 

 direct link between the earliest placental and im- 

 placental mammals, and their common' ancestor, if 

 indeed they had one, and are not independently 

 descended from amphibian or_ reptilian forms also 

 unknown. 



The only family which conspicuously distinguishes 

 the Mesozoic age is that of the Cycads ; the modern 

 Cycads survive only in hot climates, though in such 

 a manner as to show their original universal distribu- 

 tion ; they are found in Africa, India, Japan, ?tIexico, 

 and the West Indies. In Mesozoic times they 

 flourished in Greenland and at .-Spitzbergen, and 

 indeed vegetation seems to have flourished equally 

 well from the Arctic Circle to the Equator, and to 

 have been alike all over the known world from 

 Siberia to India. The Cycads are well-known objects 

 in our hothouses, with their short fat stems and 

 crown of fern-like leaves. In the celebrated "dirt- 

 beds " of Portland, the Cycads seem to have formed 

 the undergrowth to the forest of pines, and their 

 short thick stems are known to the quarrymen as 

 "fossil birds' nests." Even the Cycads had their 

 precursors in the fern-like leaved Noeggerathia of the 

 Carboniferous, and are themselves related to the 

 higher exogens by the structure of their stems. There 

 is, however, no real advance in the type of vegetation 

 till we reach the Lower Cretaceous deposits, when the 

 genus Sequoia makes its appearance, and with it the 

 true cone-bearing pines. 



The history of the Sequoias is most interesting ; 

 the genus Sequoia is now only represented by two 

 species, one the celebrated " Big- tree" of California, 

 and the other the Redwood of the Pacific slopes in 

 California and Oregon. 



The Sequoias present a striking instance of appa- 

 rently sudden development, analogous to the ap- 

 parently equally sudden development of important 

 orders of mammals in the Eocene. In the Cretaceous 

 strata Sequoia appear with twenty-six species, four- 

 teen of which are found in the Arctic zone. The 

 genus was then, and is now, the grandest represen- 

 tative of the whole family of Conifers ; the last 

 remnant of Sequoia gigantea (Wellingtonia) contains 



some of the largest trees that have ever grown on 

 earth, the tallest now standing measuring a height of 

 325 feet, and a girth of from 50 to 60 feet. In the 

 case of one of the trees the number of rings of 

 growth indicated an age of about 1300 years. The 

 Redwood of California and Oregon {Sequoia sem- 

 pei-vireiis) is only second to Sequoia gigantea in height, 

 some of the trees measuring 300 feet. The seeds of 

 both these giant pines have been brought to Europe, 

 and now flourish there. In Tertiary times, however, 

 the Sequoias required no importation, for their fossil 

 remains have been found at Spitzbergen in 78° 

 north latitude ; at Atanekerdluk in Greenland, in 

 70" N. ; in Devonshire at Bovey Tracey (a species 

 resembling Wellingtonia) ; in the Hebrides ; on the 

 Rhone ; in Italy and Germany ; and in Asia can be 

 traced along the Siberian steppes to Possiet, to the 

 coast of the Sea of Japan, and across to Alaska and 

 Sitka. Their remains constitute the largest part of 

 the great Lignite Tertiary deposits of the Canadian 

 North- West. 



In the Jurassic period the earliest known examples 

 of endogenous plants are found, bamboo and screw- 

 pine like forms. The screw-pine or pandanus is 

 really a humble relation of the palms. Some 

 species of pandanus have fragrant blossoms, and 

 with the endogens must have come gradually a 

 world with flowers. It is not therefore surprising 

 to find that in the higher portion of the Jurassic 

 series we have a true butterfly (allied to the tropical 

 American genus Brassolis). Strangely enough in 

 this same Upper Jurassic series are found the humble 

 beginnings of several of the highest forms of life, the 

 first butterfly, the first bird and the earliest mammals, 

 all probably appearing to the last degree insignificant 

 amid the teeming life around them. 



The extraordinary development of the highest 

 forms of plants and animals did not take place 

 simultaneously. The dicotyledonous angiosperms 

 (oaks, maples, beeches, &c.) which represent the 

 highest possibilities of plant, as the placental mam- 

 mals do of animal, life, appeared in the Upper 

 Cretaceous. 



[To be continued.) 



TRICHODINA— A STUDY AMONG THE 

 INFUSORIA. 



THE Infusoria at one time included a large 

 number of microscopic animals of varying 

 degrees of organisation, and not only did it include 

 animals, but also what we now believe to be plants. 

 Since then the term has been restricted to a class of 

 the Protozoa, the lowest of the great animal sub- 

 kingdoms. No differentiation into cells exists in the 

 members of this class ; they are furnished with one 

 or more vibratile cilia, and possess a nucleus ; they 

 reproduce themselves by division or, in some cases at 



G 2, 



