26 THE MODERN STUDY OF ZOOLOGY 



most important of which are the tendency to shorten 

 the processes of development, thereby causing the 

 omission of stages which may be of extreme his- 

 torical significance ; and, secondly, modifications 

 introduced by natural selection into the ontogenetic 

 history in consequence of the struggle for existence 

 which free-living larvae have, in common with adult 

 forms, to undergo. 



Thus, in spite of the powerful aid afforded us by 

 embryology, our problem is still one of extreme 

 difficulty, requiring for its solution great patience, 

 great manipulative skill, and, above all, the faculty 

 of distinguishing accurately between essentials and 

 accidentals. A good beginning has already been 

 made, mainly through the energy of zoologists in 

 other countries than our own. England has not 

 yet contributed her fair share towards the solution 

 of a problem the conception of which was first ren- 

 dered possible by the magnificent labours of one of 

 the greatest of her children, Charles Darwin. 



