250 NATURAL SCIENCE [October 



(7) That when not required in cell development they will tend 

 to pass into the system of the organism, and that when 

 suitable conditions arise they will tend to reproduce the 

 cells from which they are derived. 



In the earlier forms of life these units will diffuse themselves 

 throughout the organism (Protozoa), but as differentiation occurs 

 these units will tend to become localised at one or more places 

 (Hydrozoa). Of these places one will become more important 

 either from habit or position, and this will become fixed and 

 subsequently specialised (ovary or testis). The cell differentiation 

 will at last become so great that it will stop all reproduction of 

 parts except at the specialised centre. Partial renewal of limbs, etc. , 

 in the earlier vertebrates becoming rarer and ceasing altogether as 

 we ascend to the higher vertebrates. 



x &" 



(8) That these reproductive units having once started a 



phenomenon in any given direction, the direction will tend 

 to be kept up and continued by physiological laws. 



(9) That each unit would tend from habit to occupy in a new 



organism a position similar to that which it occupied in 

 the parent. 



This theory would explain the constancy of type, as there 

 would be a continually increasing balance in favour of heredity. It 

 would satisfactorily explain the recapitulation theory of embryology. 

 It would account for the recognised antagonism existing in both 

 plants and animals between the reproductive and bodily growth, and 

 it would afford an explanation of growth in abnormal situations. 



In conclusion, I think it will be found that we are brought 

 back to a closer study of the causes of variations as the only 

 satisfactory means of solving the fundamental problem of use- 

 inheritance. J. Lionel Tayler. 



