28O EVOLUTION OF TO-DAY. 



It may sometimes happen, however, that gemmules 

 arising in the female might find their way into the 

 ovum directly. If so, the ovum would be directly 

 modified without the interference of the male, and 

 an acquired variation of the female would be trans- 

 mitted. The male element is, however, specialized 

 to collect these gemmules, and therefore the varia- 

 tions arising through the male will be much more 

 numerous. Finally, Brooks assumes, and this is the 

 important part of the hypothesis, that, although 

 every part of the body has the power of giving rise 

 to these gemmules, under ordinary circumstances this 

 does not occur. So long as any part of the body is 

 in perfect harmony with its surroundings, it simply 

 performs its functions without giving off gemmules. 

 But just as soon as unfavorable circumstances occur 

 for the organ, gemmules arise, which, finding their 

 way into the male sexual bodies, and hence into the 

 ovum, affect the corresponding organ of the next 

 generation. For example, let us suppose some ter- 

 restrial animal to change its habits of life and begin 

 to live in the water. Its eyes, which had previously 

 been adapted to the air, are, of course, unfitted for 

 water. These unfavorable conditions cause the ani- 

 mal to strain its eyes in using them, and this strain 

 causes the various parts to throw off gemmules. 

 These gemmules find their way into the spermato- 

 zoon, and hence, at fertilization, into the ovum. 

 Here, by their affinity, they affect that part of the 

 ovum which is to give rise to the eyes of the next 

 generation, and this will cause an immediate devel- 

 opment of a large amount of variability in the eye. 



