5G0 THE PROBLEMS OF HEREDITY AND THEIR SOLUTION. 



deep ignorance tilmcst of the outline of the facts, observations care- 

 fully planned and faithfully carried out for ev^eu a few3a^ars ma}' pro- 

 duce results of great value. In fact, by far the most appreciable and 

 definite additions to our knowledge of these matters have been thus 

 obtained. 



There is besides some misapprehension as to the kind of knowledge 

 which is especialh'^ wanted at this time, and as to the modes ])y which 

 we ma}' expect to obtain it. The present paper is written in the hope 

 that it may in some degree help to clear the ground of these difficul- 

 ties by a preliminary consideration of the question, How far have we 

 got toward an exact knowledge of heredity, and how can we get 

 farther 'i 



Now, this is preeminently a subject in which we must distinguish 

 what we can do from what we want to do. We want to know the 

 whole truth of the matter; we want to know the physical Ijasis, the 

 inward and essential nature, "the causes," as they are sometimes 

 called, of heredity; but we want also to know the laws which the out- 

 ward and visible phenomena obey. 



Let us recognize from the outset that as to the essential nature of 

 these phenomena we still know absolutely nothing. We have no 

 glimmering of an idea as to what constitutes the essential process by 

 which the likeness of the parent is transmitted to the offspring. AVe 

 can study the processes of fertilization and development in the finest 

 detail which the microscope manifests to us, and we may fairly say 

 that we have now a considerable grasp of the visible phenomena; ])ut 

 of the nature of the physical basis of heredity we have no conception 

 at all. No one has yet any suggestion, working hypothesis, or mental 

 picture that has thus far helped in the slightest degree to penetrate 

 beyond what we see. The process is as utterly mysterious to us as a 

 flash of lightning is to a savage. We do not know what is the essen- 

 tial agent in the transmission of parental characters, not even whether 

 it is a material agent or not. Not only is our ignorance complete, but 

 no one has the remotest idea how to set to work on that part of the 

 problem. We are in the state in which the students of physical science 

 were in the period when it Avas open to anyone to believe that heat 

 was a material substance or not, as he chose. 



But apart from any conception of the essential modes of transmis- 

 sion of characters, we can study the outward facts of the transmission. 

 Here, if our knowledge is still very vague, we are at least beginning 

 to see how we ought to go to work. Formerly, naturalists were con- 

 tent with the collection of numbers of isolated instances of transmis- 

 sion — more especially, striking and peculiar cases — the sudden appear- 

 ance of highly prepotent forms, and the like. We are now passing 

 out of that stage. It is not that the interest of particular cases has in 

 any way diminished^ — for such records will always have their value — 



