INFECTION OF THE GAMETES 137 



definitely that the ovum or sperm may be infected with a 

 parasitic micro-organism ; that the ovum may be infected 

 after fertilisation ; and that the embryo may be infected 

 before birth. Thus with syphilis the micro-organism of 

 the disease (a spirochete) may have found its way into the 

 sperm cells of the male parent, or into the ova of the female 

 parent. That this is the case, is shown very clearly by the 

 fact that a woman may bear a syphilitic child without ex- 

 hibiting any of the symptoms of the disease herself. In any 

 case, there is not a shadow of evidence to support the view 

 that the disease acquired by the parents is transmitted to 

 the offspring. What the evidence shows is, that the ovum, 

 or sperm, or embryo, is directly infected by the spirochete. 



The cells of Hydra viridis, a very simple multicellular 

 animal living in fresh water, contain a large number of 

 minute green bodies. These are Algx, unicellular plants. 

 Now these Algte are present in the eggs of Hydra before 

 the organism begins to develop, but they are not present 

 in the earliest stages of the maturation of the egg. As the 

 cells of Hydra multiply, so the Algse multiply and live 

 within them. This case affords an excellent illustration of 

 the way in which ova or sperms may be infected with the 

 parasites of disease, although the presence of the Algie in 

 the cells of Hydra cannot be regarded as a disease, as they 

 do no harm to the animal. 1 



A case which seems to suggest a definite influence of the 

 environment upon the germ cells has been recorded in some 

 experiments upon a species of Daphnia, a minute crustacean 

 living in fresh water. Salt was gradually introduced into 

 the water in which the Daphniie were living. In forty-five 

 days the water contained 1/5 per cent, of salt, and at this 

 time all the adults died. Some of the eggs, however, con- 

 tinued to live, hatched out, and the offspring did well. 2 At 

 first sight it would appear that the probable explanation of 



1 Zeigler, H. E., Die Vcrerbungslehre in der Biologic, Fischer, Jena, 1905. 



z Packard, A. 8., " On the Inheritance of Acquired Characters in Animals 

 with a Complete Metamorphosis," Proceedings of the American Academy of 

 Science, xxix., 1894. 



