SCIENCE. 



[N. S. Vol. XL No. 284. 



duction, but not always, for in certain 

 fungi* fusion of hyphse and consequent 

 intermingling of protoplasm occurs, and is 

 not followed by any form of reproduction. 

 Among bacteria alone, so far as I know, 

 has the phenomenon of conjugation never 

 been observed. 



To sum up, we have seen that the phe- 

 nomenon of conjugation is very widely dis- 

 tributed. Excluding the bacteria, there is 

 reason to believe that it forms a part of the 

 vital phenomena of all organisms. Its es- 

 sential features are a mixture and fusion of 

 the protoplasm of two different organisms, 

 accompanied by a fusion of their nuclei. 

 It results in the formation of a new indi- 

 viduality, which differs from the individu- 

 alities of both the conjugating organisms. 

 This difference manifests itself in differences 

 in habit, constitution, form and structure ; 

 such differences constituting what we have 

 called genetic variations. 



The conjugation of the ovum and sper- 

 matozoon in the higher animals, and the 

 corresponding process in the higher plants, 

 are special cases of this conjugation, in 

 which special conjugating individuals are 

 produced, the ordinary individuals being 

 physically incapable of the process. The 

 phenomenon of sex, with all its associated 

 complications, which is so characteristic of 

 the higher animals and plants, is merely a 

 device to ensure the coming together of the 

 two gametes. In the lower animals it is 

 possible for the ordinary organism to con- 

 jugate: consequently the phenomenon does 

 not form the precursor of developmental 

 change, and is in no way associated with re- 

 production. Indeed, in such cases it is often 

 the opposite of reproduction, inasmuch as 

 it brings about a reduction in the number 



* It must be mentioned, however, that in the case 

 of these fungi the fusion of nuclei has not been ob- 

 served, nor has it been noticed whether the habit, 

 structure, or constitution of the conjugating plants 

 are altered after the fusion. 



of individuals two separate individuals fus- 

 ing to form one. 



ACQUIRED CHAEACTEES. 



We now come to the consideration of the 

 second kind of variations — namely, those 

 which owe their origin to the direct action 

 of external agencies upon the particular 

 organism which shows the variation ; or, as 

 Darwin puts it, to the definite action of ex- 

 ternal conditions. These are the variations 

 which I have called acquired variations or 

 acquired characters. This is not a good 

 name for them, but at the present moment, 

 when I am about to submit them to a criti- 

 cal examination, I do not know of any other 

 which could be suitably applied. Later on, 

 when I sum up the various effects of the 

 direct action of external agencies upon the 

 organism, I may be able to use a more suit- 

 able term. 



The main peculiarities of acquired varia- 

 tions are two in number : (a) they make 

 their appearance as soon as the organism 

 is submitted to the changed conditions ; (6) 

 speaking generally they are more or less the 

 same in all the individuals of the species 

 acted upon. As examples of this kind of 

 variations, I may mention the effect of the 

 sun upon the skin of the white man ; the 

 Porto Santo rabbit, an individual of which 

 recovered the proper color of its fur in four 

 years under the English climate ;* the 

 change of Artemia salina to Arteniia milJiau- 

 senii ; the increase in size of muscles as the 

 result of exercise ; and the development of 

 any special facility in the central nervous 

 system. Among plants, variations of this 

 kind are very easily acquired, by altering 

 the soil and climate to which the individ- 

 uals are submitted. So common are they, 

 that it is quite possible that a large number 

 of species are really based upon characters 

 of this kind ; characters which are produced 

 solely by the external conditions and which 

 * Darwin, Variation, ed. 2, Vol. I., p. 119. 



