CHAPTER XVI 



Conclusion 



IN most of the preceding chapters some sort of summary 

 has been given of the main results that have been arrived 

 at in the branches of the subject with which they deal, and 

 the purpose of this final chapter is not to give any general 

 summary of results, but rather to look forward and to note 

 the various directions in which investigation is progressing 

 or is especially needed. 



Cytology, in the sense in which the word is usually under- 

 stood, has in the past been very largely a morphological 

 and descriptive science; its aim has been to observe the 

 structure of cells, to determine the parts of which they are 

 composed, and to describe the changes through which they 

 pass in the various phases of rest and of division. But as 

 in other branches of biology, the study of morphology 

 inevitably leads on to that of function. Anatomy is a neces- 

 sary precursor of physiology, if the conclusions of physiology 

 are to be more than superficial, but anatomy alone is an 

 unsatisfying study if the functions of the organs remain 

 unknown. And even more than the grosser anatomy of 

 animals, cytology forces on its students the continual de- 

 mand for explanation either in terms of function or by 

 means of the still more fundamental laws of physics and 

 chemistry. For, at least since the general acceptance of the 

 principle of evolution, comparative anatomists have at times 

 been content with purely morphological study, in the belief 

 that they could thereby discover the phylogenetic relation- 

 ships of different animal groups. But the science of com- 

 parative cytology is almost non-existent, with the result that 



