HEREDITY. 253 



The limitation of Heredity by sex, cannot yet be regarded 

 as established. While in many cases it seems clearly mani- 

 fested ; it is in other cases manifested to a very small degree, 

 if at all. In Mr Sedgwick's essays, already named, will be 

 found evidence implying that there exists some such tendency 

 to limitation, which does or does not show itself distinctly, 

 according to the nature of the organic modification to be 

 conveyed. But more facts must be collected before any 

 positive conclusion can be reached. 



84. A positive explanation of Heredity is not to be expected 

 in the present state of Biology. We can look for nothing beyond 

 a simplification of the problem ; and a reduction of it to the 

 same category with certain other problems which also admit 

 of hypothetical solution only. If an hypothesis which certain 

 other wide-spread phenomena have already thrust upon us, 

 can be shown to render the phenomena of Heredity more in- 

 telligible than they at present seem, we shall have reason to 

 entertain it. The applicability of any method of interpreta- 

 tion to two different but allied classes of facts, is evidence of 

 its truth. 



The power which organisms display of reproducing lost 

 parts, we saw to be inexplicable except on the assumption 

 that the units of which any organism is built have an innate 

 tendency to arrange themselves into the shape of that organ- 

 ism ( 65). We inferred that these units must be the pos- 

 sessors of special polarities, resulting from their special struc- 

 tures ; and that by the mutual play of their polarities they are 

 compelled to take the form of the species to which they belong. 

 And the instance of the Begonia phyllornaniaca left us no 

 escape from the admission that the ability thus to arrange 

 themselves, is latent in the units contained in every undiffer- 

 entiated cell. Quite in harmony with this conclusion, 



are certain implications since noticed, respecting the characters 

 of sperm-cells and germ-cells. We saw sundry reasons for 

 rejecting the supposition that these are highly-specialized celld 



