THE GERM-PLASM 57 



germ-cells. In some of the lower animals the same power 

 of producing gametes seems to exist in most of the cells 

 of the body, but when we come to the higher animals the 

 germ-plasm is generally separated from the rest of the 

 body at a comparatively early stage in the development 

 of the individual. 1 The fact that if the cells be shaken apart 

 when the ovum has divided into two or more, even into as 

 many as sixteen, each of them is capable of producing an 

 embryo complete in all its parts, also suggest the existence 

 of germ-plasm in all the cells of the body, in some organisms 

 at any rate. 2 



It is quite possible that in some cases the germ -plasm is 

 separated off at an early stage in the development of the 

 organism. It seems quite certain that in other cases this 

 does not happen. The period at which the germ-plasm 

 emerges is not of vital importance, nor is it essential to 

 assume that it is always limited to a particular group of 

 cells in all organisms. Weismann's main points are not 

 seriously affected. It still remains quite possible, or even 

 probable, that the germ-plasm continues independently, that 

 inborn variations .arise only in the germ-plasm itself, that 

 there is no transmission of any characters from parent to 

 offspring except those existing germ -plasm, and there is no 

 necessity to believe that acquired characters may be trans- 

 mitted because Weisrnann's original theory is thus modified 

 with regard to some details. 



1 It is interesting to note, in relation to Hertwig's theory, that the cells of 

 cancer in man and other vertebrates have been described as presenting veiy 

 many important points of resemblance to germ-cells. For instance, reduction is 

 said to take place among them, and several other phenomena generally only 

 found in such cells as are about to produce mature gametes. Fanner, Moore, 

 and Walker, "On the Resemblances exhibited between the Cells of Malignant 

 Growths in Man and those of Normal Reproductive Tissues," Proc. Roy. Soc., 

 vol. Ixxii., 1903 ; " On the Resemblances existing between the Plimmer's Bodies 

 of Malignant Growths and certain Normal Constituents of Reproductive Cells in 

 Animals," Proc. Roy. Soc., B. vol. Ixxvi., 1905 ; "On the Cytology of Malignant 

 Growths," Proc. Roy. 8oc., B. vol. Ixxvii., 1906. 



2 Identical twins developed from one ovum and polyembryony in plants, 

 also suggest that the separation of the germ-plasm does not occur at the first 

 segmentation of the ovum. 



