44 PROTOZOA CHAP. 



or on the sides of the tube : in neither case did living organisms 

 appear, even after the lapse of months. Other observers suc- 

 ceeded in showing that the forms and characters of species were 

 as constant as in Higher Animals and Plants, allowing, of course, 

 for such regular metamorphoses as occur in Insects, or alter- 

 nations of generations paralleled in Tapeworms and Polypes. 

 The regular sequences of such alternations and metamorphoses 

 constitute, indeed, a strong support of the " germ-theory" — the 

 view that all Protista arise from pre-existing germs. It is to 

 the Eev. W. H. Dallinger and the late Dr. Charles Drysdale 

 that we owe the first complete records of such complex life- 

 histories in the Protozoa as are presented by the minute 

 Flagellates which infest putrefying liquids (see below, p. 116 f). 

 The still lower Schizomycetes, the " microbes " of common speech, 

 have also been proved by the labours of Ferdinand Cohn, von 

 Koch, and their numerous disciples, to have the same specific 

 constancy in consecutive generations, as we now know, thanks 

 to the methods first devised by De Bary for the study of Fungi, 

 and improved and elaborated by von Koch and his school of 

 bacteriologists. 



And so to-day the principle "omne vivum ex vivo" is 

 universally accepted by men of science. Of the ultimate origin 

 of organic life from inorganic life we have not the faintest 

 inkling. If it took place in the remote past, it has not been 

 accomplished to the knowledge of man in the history of scientific 

 experience, and does not seem likely to be fulfilled in the 

 immediate or even in the proximate future.-' 



PEOTOZOA 



Organisms of various metabolism, formed of a single cell or 

 a'pocyte, or of a colony of scarcely differentiated cells, whose organs 

 are formed hy differentiations of the protoplasm and its secretions 

 and accretions ; not composed of differentiated multicellular tissiies 

 or orga7is} 



' Dr. H. Charlton Bastian has recently maintained a contrary thesis (The 

 Nature, and Origin of Living Matter, 1905), but has adduced no evidence likely to 

 convince any one familiar with the continuous life-study of the lower organisms. 



^ The terms "organoid," "organella," have been introduced to designate a 

 definite portion of a Protist specialised for a definite function ; the term " organ " 



