146 EVOLUTION OF TO-DAY. 



They are, therefore, as truly engaged in a struggle 

 for existence as the adult. Now, since these larvae 

 are known to be subject to variation, there is no 

 reason why the action of the environment should 

 not modify them as much as it does the perfectly- 

 developed insect. If this occurs, the larvae immedi- 

 ately begin to depart from the typical form, and the 

 embryological history is much modified. Abundant 

 instances of this occur in Echinoderms, Crustacea, 

 and insects. We see, therefore, that the embryologist 

 has to deal with modifications arising from a station- 

 ary, dependent condition of the embryo, and others 

 arising from its free, independent existence. Neither 

 the direct nor indirect development can be implicitly 

 relied upon. It would almost seem, therefore, that 

 here was a bar to further advance. Some biologists 

 have expressed themselves as out of sympathy with 

 any further reasoning after the great falsification of 

 the record is once admitted. But the difficulty is 

 not so great as it seems. Undoubtedly, such modi- 

 fications exist, and the only question is as to the 

 ability of the student, with the evidence at his com- 

 mand, to recognize them. Of course, this cannot 

 be done from single specimens, but it has been 

 found possible in many cases, by the collection of 

 great masses of data, to straighten effectually the 

 evidence and get some logical results. But it is 

 certainly necessary to withhold any conclusions 

 until we can get all of the evidence possible from 

 every source, in expectation that when all comes to 

 be considered together the truth may be plainly 

 apparent. The wiser embryologists, therefore, have 



