262 CONCLUSION [CH. 



anatomical characters. A few attempts in this direction 

 have been made. MEEK, for example, on the basis of mea- 

 surements of the thickness of chromosomes in the metaphase 

 of division, concludes that the chromosomes of the Protozoa 

 are typically 0-21 /n in width; that in those of the Coelente- 

 rata, Nemertinea and Echinodermata this width is doubled 

 (0-42 /A) and that in all the chief higher Phyla (Nemathel- 

 minthes, Annelida, Arthropoda, Mollusca and Vertebrata) 

 the width of the chromosomes is twice as great again, giving 

 an average measurement of 0-83 /x. MEEK'S conclusions have 

 been criticised on the grounds that measurements of suffi- 

 cient accuracy are hardly possible with existing methods, 

 and that the sizes of the chromosomes vary according to the 

 type of cell examined, but whether his results are substan- 

 tiated or not, they suggest a wide and important field for 

 further research. Comparative anatomy provides one of the 

 chief foundations for the theory of evolution, and it can 

 hardly be doubted that by a comparative study such as 

 MEEK has made of a few forms and in respect of only certain 

 characters, new and valuable information could be obtained 

 with regard to the evolution of cell structure. 



The successful prosecution of such investigations might 

 lead very far towards a solution of one of the most funda- 

 mental and mysterious problems of biology, that of the 

 nature of the earliest forms of living organisms. It has often 

 been assumed that the first forms of life were composed 

 of simple protoplasm, comparable with the most undiffer- 

 entiated cytoplasm of simple embryonic cells. But this is 

 a pure assumption; no such organism or undifferentiated 

 cell is known, and it may be that in supposing life to have 

 first arisen in a form of this kind, speculative biologists have 

 been looking in the wrong direction. Present cytological 

 knowledge gives little support for such a hypothesis, and 



