ZOOLOGY. 343 



tematic purposes, would afford the best idea of the nature of these difficulties. 

 The definition of Linnaeus, that minerals grow, plants grow and live, and 

 animals grow, live, and feel, was first examined. In order to apply this defi- 

 nition, the terms growth, life and feeling, required explanation. Growth simply- 

 indicated increase. The term life could not be defined in such a manner as 

 to render it inapplicable to the physical phenomena of the inorganic world, 

 and at the same time embrace the lowest forms of organized beings. Feeling 

 could not be defined so as to separate the movements evinced by so many 

 members of the vegetable kingdom, on the application of external stimulant.-, 

 as the movements of the leaves of the sensitive plant, and the closing i;i:.> 

 unfolding of flowers, from those of the animal kingdom. Such were the dis- 

 tinctions attempted to be made by one who disregarded the use of the micro- 

 scope. 



One of the most obvious distinctions between the organic and inorganic 

 kingdoms was the presence of the cell in the former. Under some circum- 

 stances it was not easy to detect the cell, as in certain fossils, and sometimes 

 inorganic matter assumed a cellular form. Another distinction adopted by 

 naturalists, even since the general introduction of the microscope into natural 

 history inquiries, was, that animals moved, while plants were fixed. This 

 distinction, though applicable to the higher forms of plants and animals, was 

 more than ever applicable to the organisms which required the microscope to 

 detect their existence. Recent researches had shown that the motile tissues 

 in animals were composed of the same substance that was found to be present 

 in the cells of all plants, and which under the names of nucleus, cytoblast, 

 primojftial utricle, and endoplast, had been recognized by all vegetable physi- 

 ologists. This substance composed of protein, was as actively motile in the 

 plant as in the animal. It was this substance that gave motility to the cells 

 of protococcus, the fibers of oscillaria, the spores of various Confervas and 

 fungi, and probably also to all other movements observed among plants. 

 "When cilia were originally discovered as the agents of movement in infusoria, 

 and upon the internal organs of higher animals, they were regarded as 

 characteristic of animal life. These organs were now known to be present 

 in the zoospores of various Confervse, and were active agents of movement 

 hi the Yolvox globator, of whose vegetable nature there could be but little 

 doubt. 



The possession of what were called eye-spots in doubtful organisms had 

 been brought forward to decide the animality of these beings. Such eye- 

 spots as present red points in certain stages of the growth of volvox, and 

 other undoubtedly vegetable organisms, and according to Henfrey, were due 

 to the relation of the contents of the cell to light, were in no way the 

 agents of vision hi the cells in which they are found. The definition of Aris- 

 totle, that animals possessed a mouth, while plants had none, had recently 

 been revived ; and of all merely structural characters it was the one best 

 suited to the purpose of the naturalist. Until recently the exceptions to this 

 definition were numerous ; but since the botanist had claimed so large a num- 

 ber of mouthless infusoria, it was more than ever applicable. There were 

 however exceptions, and these are found in the Foraminifera, and other low 



