6 

 OUTLOOK 



Perhaps it may be allowed that the absence of a complete and unified 

 synthesis of mitosis in the foregoing pages is not wholly due to the 

 shortcomings of the authors' presentation of the subject. Much still 

 remains to be elucidated before it will be possible to construct one, and 

 the student entering this field need fear no lack of problems. There 

 are indeed, as Dr Johnson said of Spain, parts that have not been 

 perambulated. 



Not all the unexplored regions of the subject are inaccessible; there 

 are some which happen merely to be off the main tracks of investigation 

 trodden by those who follow particular ideas, or exploit favourable 

 sources of material. These highways may perhaps be classified in the 

 following fashion. 



Cytogenetical — The underlying theme of the majority of papers in 

 cytology for most of the last 50 years has been the correlation of the 

 experimental study of inheritance with the behaviour of the chromo- 

 somes within the cell. Indeed, cytology is sometimes equated with 

 cytogenetics. Somatic mitosis is only one of many topics in this subject, 

 and in these pages no attempt has been made to discuss any of the 

 others, full though they are of detailed observations on the cell. The 

 cytoplasmic aspects of mitosis however tend not to be included. 



Comparative — Two main objectives may be discerned in studies of 

 this kind on the dividing cell. One is the classical aim of all comparative 

 anatomy, that of revealing evolutionary relationships; while the 

 other seeks a closer understanding of the common themes of mitosis and 

 meiosis by revealing the variations upon them found in different 

 organisms. 



Physiological — Under this category we can include all those lines of 

 research which deal in such a variety of ways with the living cell. For 

 several reasons, marine eggs, chiefly of Echinoderms, have been used in 

 the great majority of experimental studies on dividing cells, and recent 

 developments in several fields such as in microscopy and the use of 

 trace elements have shown that much still remains to be done with this 

 material. Other cells in which more detail can be seen in life are less 

 readily accessible to experimental analysis, though considerable 

 development is possible both in the methods of observing and in the 

 technique of experimentation on many types of living cell. 



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