FUETHEB REMARKS ON THE OELL-THEORT. 217 



■weW be considered. In the first place, the unicellular origin 

 is only found in sexual reproduction, not in asexual. The 

 characteristic of the unicellular form is its simplicity of struc- 

 ture, and the essential feature of sexual reproduction is the 

 conjugation of the reproductive cells. Now in the Protozoa, 

 in which the amount of formed tissue is generally slight and 

 the structure of the body simple, conjugation can and does 

 often take place between the ordinary form of the species. 

 But in the Metazoa, in which conjugation is as necessary a 

 phenomenon in the specific cycle as in Protozoa, conjugation 

 is impossible between adult or ordinary individuals of a species 

 from mechanical causes. How is this difiiculty got over in 

 nature ? My answer is, by the formation of special individuals 

 of extremely simple structure — a structure so simple that conju- 

 gation between them is possible. To put the matter in another 

 way, I should regard the ordinary dioecious Metazoon as a tetra- 

 morphic species, consisting of male, female, ovum, and sper- 

 matozoon, the two latter being individuals which are specially 

 produced to enable conjugation to take place. 



Mr. Bourne, in his criticism, begins by complaining that he 

 cannot ascertain from my article my own views on the subject 

 of the cell-theory. Why should he expect or wish to discover 

 them ? My remarks were simply directed to show the short- 

 comings of the theory with regard to certain anatomical facts. 

 As explained above, my own view is that the cell-theory is 

 iuadequate to explain the facts, and that it is not possible at 

 present to explain them by any theory. He proceeds to state 

 that I am abusive because I say that certain observers " are 

 constrained by this theory with which their minds are saturated, 

 not only to see things which do not exist, but also to figure 

 them " (I am referring to embryonic mesoderm of vertcr 

 brates). He calls this abuse, not argument. I venture to 

 differ with him— it is neither abuse nor argument j it is merely 

 a statement of fact (unless, indeed, it be considered abusive 

 to say that a man accepts and believes in the cell-theory). If 

 you disbelieve it, consult the memoirs of the last twenty years 

 in which this tissue is referred to, and in most of them you 



