46 MAN AN ADAPTIVE MECHANISM 



reactions essentially similar to the adaptive reactions 

 of cells in the bodies of multicellular animals. A closer 

 parallel, however, may be seen in the history of the 

 sexual elements during the process of fertilization. 

 The male and female reproductive elements differ in 

 form, the ovum being usually spherical, while the sper- 

 matozoon is generally smaller and has a rounded 

 "head" and a greatly attenuated "tail." A func- 

 tional dissimilarity corresponds to this difference in 

 form. The male element, the spermatozoon, is motile, 

 and by the lashings of its whiplike "tail" is enabled to 

 approach the non-motile ovum. In all probability 

 this phenomenon is in some cases largely due to the 

 chemotactic attraction of the sperm, though in other 

 instances the spermatozoa cease their swimming move- 

 ments when they come in contact with a smooth sur- 

 face (stereotropism). The behavior of the sperma- 

 tozoon is closely comparable with that of many 

 protozoa. 



Thus in nature processes are repeated many times 

 and usually by the same pattern. In the very lowest 

 forms of life which are devoid of any visible nervous 

 system or other specialized tissue, are manifested re- 

 actions, which, in the higher organisms, are effected 

 by the activities of some specialized structure, such 

 as the central nervous system. 



If, as we have intimated, this power of adaptive re- 

 sponse is a general function of protoplasm and if 

 "adaptive responses" constitute the sum total of 

 "mind" and "nervous reaction," we may well ask 

 of what use is a central nervous system in the life of 

 higher -organisms ; and whether, in organisms which 



