MICROSCOPIC STUDY OF ANIMAL DEVELOPMENT. 57 



But, further, the Physiologist, not confining his inquiries to 

 Man, pursues the like researches into the developmental history 

 of other living beings, and is soon led to the conclusion that the 

 same is true of them also ; each Animal, as well as each Plant, 

 having the same starting-point in the single cell ; and the dis- 

 tinctive features by which its perfected form is characterized, 

 how striking and important soever these may be, arising in the 

 course of its development towards the condition it is ultimately 

 to present. In the progress of that evolution, those fundamental 

 differences which mark out the great natural divisions of the 

 Animal and the Vegetable kingdoms respectively, are the first 

 to manifest themselves ; and the subordinate peculiarities which 

 distinguish classes, orders, families, genera, and species, succes- 

 sively make their appearance, usually (but not by any means 

 constantly) in the ordei^of importance which Systematists have 

 assigned to them. And it is in thus pursuing, by the aid which 

 the Microscope alone can afford to his visual power, the history 

 of the Organic Germ, from that simple and homogeneous form 

 which seems common to every kind of living being, either to 

 that complex and most heterogeneous organism which is the 

 mortal tenement of Man's immortal spirit, or only to that hum- 

 ble Protophyte or Protozoon, which lives and grows and multi- 

 plies without showing any essential advance upon its embryonic 

 type, that the Physiologist is led to his grandest conception of 

 the Unity and All-Comprehensive nature of that Creative Design, 

 of which the development of every individual Organism, from 

 the lowest to the highest, is a separate exemplification, at once 

 perfect in itself, and harmonious with every other. 



It has been the purpose of the foregoing sketch, to convey an 

 idea, not merely of the services which the Microscope has already 

 rendered to the collector of facts in every department of the Sci- 

 ence of Life, but also of the value of these facts as a foundation 

 for philosophical reasoning. For it is when thus utilized, that 

 observations, whether made with the Microscope or with the 

 Telescope, or by any other instrumentality, acquire their highest 

 value, and excite the strongest interest in the mind. But as it 

 is not every one who is prepared by his previous acquirements 

 to appreciate such researches, according to the scientific estimate 

 of their importance, it may be well now to address ourselves to 

 that large and increasing number, who are disposed to apply 

 themselves to Microscopic research as amateurs, following the 

 pursuit rather as a means of wholesome recreation to their own 

 minds, than with a view to the extension of the boundaries of 

 existing knowledge ; and to those in particular who are charged, 

 whether as parents or as instructors, with the direction and train- 

 ing of the youthful mind. 



All the advantages which have been urged at various times, 



