EVOLUTION. 85 



forms that are almost impossible to be separated from, 

 or are intermediate between, the two kingdoms of na- 

 ture : For instance, many of the lower forms of polyzoa 

 cannot be definitely separated from many of the alga 

 or seaweeds, which, at a certain period of growth, 

 throw out free forms having small bodies with a tail 

 at each end, and which move about freely in the 

 water. Thus the two forms, the animal and the 

 plant, are so similar that a definite study of each is 

 absolutely necessary in order to separate them with 

 any degree of satisfaction if at all. Such a study 

 has not as yet been made, and, undoubtedly, when 

 it is made, many errors in our belief concerning them 

 will be corrected, if not our whole classification of 

 them altered. Then, too, we have many animals in 

 the insect or articulate branch, which insensibly run 

 into each other and into others of other branches, 

 these are so closely allied as to be almost inseparable 

 if not quite so. Now to what does all this tend? 



"Many of the old scholars of science classified the 

 animal kingdom in such a way that there were no in- 

 termediate forms by placing the doubtful genera and 

 species in separate and distinct groups; thus repre- 

 senting the whole animal and vegetable kingdoms by 

 separate and distinct groups, also. But we see, now, 

 that this is contrary to their general structure, and 

 opposed to true classification. If we represent the 

 old classification by a series of straight lines, we 

 shall have a good illustration of the relation of the 

 old orders (or, better, branches) to each other; or 

 even if the lines are placed in an inclined direction, 

 one line being above the other, we shall still have a 

 very good representation of the way in which the ani- 

 mal kingdom was classified by the old writers, 

 though each writer represented them by a different 

 number of branches and orders: one conceding seven 

 branches and twenty-eight orders; and another, elev- 

 en branches and seventeen orders; and so on. 



"As I have said before, we know that many genera 

 run into each other in such a way that they are al- 



