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NA TURE 



\Aug. 15, 1872 



for example, have hardly undergone any essential change, 

 the same forms and varieties recurring at very distant 

 geological periods. If, however, living matter docs con- 

 tinually come into existence, the lowest forms will pro- 

 bably have been very similar in all ages ; and it is only as 



the varying conditions of the different periods will have 

 led to the development of specialised groups. 



The nature and mode of development of the low organ- 

 isms found in infusions is next elaborately discussed, with 

 the following result : — "No other conclusion remains for 



these forms developed into more complex organisms that us, but that the several organisms are products of the 



Fig. 3. — Mode of Origin of Paramecia— (x Soo). 

 First stage of differentiation. /'. Later stage, in which vacuole ha^ appeared, b^. Similar stage of much larger embryo, 

 has segmented into four (only three parts visible), c. Later stage : embryo filled with large particles, and revolving 

 : after it emerges from its cyst, e, Nassula-\)S^^ form into which many afterwards passed. 



Another embryo \ 

 hin its cyst. d. 1 



direct developmental unfolding of new-born specks of 

 living matter. And yet among these forms we see Bac- 

 teria, Vibriones, Leptothrix, and Torukc ; Fungus fila- 

 ments, with and without fructification ; Protamceba: and 

 flagellated Monads ; Pediastrea: and Algoid filaments. 

 All these are therefore proved with the greatest certainty 

 to be interchangeable forms, which may be assumed on 

 different occasions by newly evolved specks of living 

 matter." Evidence is also adduced of the changes in other 



low forms. Green corpuscles thrown off from a single 

 Lichen have been seen by Dr. Hicks to assume the forms 

 and mode of growth characteristic of no less than twenty- 

 three supposed species of Algic ; while gonidia from an 

 Alga or from a Moss were developed into Lichens, Alga;, 

 or Mosses, according to the conditions under which they 

 were placed, while they may sometimes give birth even to 

 active Monads. 



Having clearly proved that Bacteria and other low 



Flo. 4.— Heterogenetic Origin or Monads from Nr 

 Contents of new-formed cyst separating into Protoplasm and dark brown refuse matt 

 which afterwards escape from the ruptured cyst, e, /, g. BiffercnL forms of the Mona 

 Monads subsequently : 



LA (CaKTER)-(x 350)- 



/', r, cL Segmentation of the Protoplasm into Monads, 

 //, /, J. Forms of Amtxba; and Actinophrys which the 



organisms, which form a pellicle on the surface of infu- 

 sions and other liquids, arc produced de novo in such in- 

 fusions, the third part of the work, entitled " Hetcro- 

 genesis," is devoted to a history of the microscopical 

 examination of the changes which take place in this 

 pellicle, and of all that is at present known of the trans- 

 formations of the various classes of organisms to which it 

 gives birth. To make this part of the subject clearly in- 

 telligible, it will be necessary to reproduce a considerable 

 number of the woodcuts by which these changes are illus- 

 trated. One of the most simple series of changes— this 

 transformation of motionless corpuscles into ordinary 



Amceba: — was closely watched by Dr. Bastian, and seen 

 with the most perfect distinctness in thousands of in- 

 stances. Fig. 4 shows the stages by which the more 

 highly organised Monads are developed. The first step 

 was an increase of the amount of gelatinous matter between 

 the corpuscles or Bacteria, which gradually became less 

 defined, and at last scarcely visible in the protoplasmic 

 mass, in which segmentation then began to take place, 

 and continued till it separated into active Monads. After 

 a time, however, these again began to change into Amoeba;, 

 and these latter, passing through a motionless and encysted 

 stage, became resolved into Bacteria (Fig. 5). The whole 



