156 Animal Life and Intelligence. 



the same characters; (2) that the first polar cell leaves 

 the germinal matter unaffected, merely getting rid of 

 formative body-plasm ; (3) that the nuclear division giving 

 rise to the second polar cell is v unequal and dissimilar, 

 effecting the differential reduction of ancestral germ- 

 plasms. Concerning all of which one can only say that 

 it may be so, but that there is not much evidence that it 

 is so. And, without strong confirmatory evidence, it is 

 questionable whether we are justified in assuming these 

 three quite different modes of nuclear division. 



There remains one more question for consideration, on 

 the hypothesis that the germ-cells cannot in any special 

 way be affected by the body-cells. In considering the 

 union of ovum and sperm as a source of variation, we have 

 taken for granted the existence, of variations. We have 

 been dealing with the mixture or combination of already 

 existing variations. How were variations started in the 

 first instance ? 



We have already seen that in the protozoa parent and 

 offspring are still, in a certain sense, one and the same 

 thing ; the child is a part, and usually half, of the parent. 

 If, therefore, the individuals of a unicellular species are 

 acted upon by any of the various external influences, it is 

 inevitable that hereditary individual differences will arise 

 in them ; and, as a matter of fact, it is indisputable that 

 changes are thus produced in these organisms, and that 

 the resulting characters are transmitted. Hereditary 

 variability cannot, however, arise in the metazoa, in which 

 the germ-plasm and the body-plasm are differentiated and 

 kept distinct. It can only arise in the lowest unicellular 

 organisms. But when once individual difference had been 

 attained by these, it necessarily passed over into the 

 higher organisms when they first appeared. Sexual repro- 

 duction coming into existence at the same time, the 

 hereditary differences were increased and multiplied, and 

 arranged in ever-changing combinations. Such is Pro- 

 fessor Weismann's solution of the difficulty, told, for the 

 most part, in his own words, 



