2 INTR OD UCTION 



of the Lamarckian period gave little heed to the finer details of 

 internal organization. They were concerned mainly with the more 

 obvious characters of plants and animals their forms, colours, 

 habits, distribution, their anatomy and embryonic development 

 and with the systems of classification based upon such characters ; 

 and long afterwards it was, in the main, the study of like characters 

 with reference to their historical origin that led Darwin to his splen- 



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Fig. I. A portion of the epidermis of a larval salamander {Amblystoma) as seen in slightly 

 oblique horizontal section, enlarged 550 diameters. Most of the cells are polygonal in form, con- 

 tain large nuclei, and are connected by delicate protoplasmic bridges. Above x is a branched, 

 dark pigment-cell that has crept up from the deeper layers and lies between the epidermal cells. 

 Three of the latter are undergoing division, the earliest stage (spireme) at a, a later stage (mitotic 

 figure in the anaphase) at ^.showing the chromosomes, and a final stage (telophase), showing 

 fission of the cell-body, to the right. 



did triumphs. The study of microscopical anatomy, on which the 

 cell-theory was based, lay in a different field. It was begun and long 

 carried forward with no thought of its bearing on the origin of living 

 forms; and even at the present day the fundamental problems of 

 organization, with which the cell-theory deals, are far less accessible 

 to historical inquiry than those suggested by the more obvious 

 external characters of plants and animals. Only within a few years, 



