48 PROFESSOR A. M. MARSHALL. 



One thing above all is apparent, that embryologists must not work 

 single-handed, and must not be satisfied with an acquaintance, how- 

 ever exact, with animals from the side of development only ; for 

 embryos have this in common with maps, that too close and too 

 exclusive a study of them is apt to disturb a man's reasoning power. 



Embryology is a means, not an end. Our ambition is to explain in 

 what manner and by what stages the present structure of animals has 

 been attained. Towards this embryology affords most potent aid ; 

 but the eloquent protest of the great anatomist of Heidelberg must be 

 laid to heart, and it must not be forgotten that it is through com- 

 parative anatomy that its power to help is derived. 



What would it profit us, as Gegenbaur justly asks, to know that the 

 higher vertebrates when embryos have slits in their throats, unless 

 through comparative anatomy we were acquainted with forms now 

 existing in which these slits are structures essential to existence? 

 Anatomy defines the goal, tells us of the things that have to be 

 explained ; embryology offers a means, otherwise denied to us, of 

 attaining it. 



Comparative anatomy and palaeontology must be studied most 

 earnestly by those who would turn the lessons of embryology to best 

 account, and it must never be forgotten that it is to men like Johannes 

 Miiller, Stannius, Cuvier, and John Hunter, the men to whom our 

 exact knowledge of comparative anatomy is due, that we owe also the 

 possibility of a science of embryology. 



