XII.] CONJUGATION AND SEXUAL REPRODUCTION. 1 95 



may not also take place in the form of a fusion of two indi- 

 viduals among the non-nucleated animals, the Monera : and it 

 may be precisely here that a fusion of two whole animals 

 with a view to the mingling of characters was first effected. 

 We are acquainted with a form of conjugation in certain 

 of the Bacillariaceae, and even if it is not absolutely certain 

 that the species in question, Cocconeis pediciihts, is without 

 a nucleus, many details of the process indicate that the whole 

 mass of the organism contains the conjugating idioplasm : 

 this is chiefly suggested by the minute size of the conjuga 

 ting individuals, which invites comparison with the nucleus, 

 diminished by ' reducing divisions,' in order to facilitate amphi- 

 mixis. For this reason I believe that we ought not to follow 

 Maupas in constructing a general definition of conjugation as 

 the fusion of nuclei. 



The Theories of Rejvivenescence and of Mingling. 



I hold that the deeper significance of every form of amphi- 

 mixis, — whether occurring in conjugation, fertilization, or in any 

 other way, — consists in the creation of that hereditary individual 

 variability which is requisite for the operation of the process of 

 selection, and which arises from the periodical mingling of two 

 individually different hereditary substances. 



That such a mingling is the immediate result of amphimixis 

 is no longer open to dispute, and perhaps at no distant date it 

 will be admitted that the variabihty I have spoken of must follow 

 as a direct consequence. It is well known, however, that many 

 and indeed the majority of scientific men, who have expressed 

 themselves on the point, hold the opinion that this mingling of 

 two hereditary substances is not the one object of amphimixis, 

 — its ultimate and most important consequence, and does not ex- 

 plain the reason why it was introduced into the organic world. 

 It is obvious that my view as to the effect of amphimixis in 

 originating variability may be perfectly correct, without the 

 essence of fertilization or of conjugation being thereby ex- 

 plained. What I regard as its chief object may after all only 

 be secondary, and the true significance of the process may lie 

 in some consequence unknown to me or which I have over- 

 looked. 



o 2 



