The Role of the Chromosomes 235 



the field of a microscopic preparation, thereby lighting 

 up quite small portions of a cell, and how these portions 

 can thereby also be heated, and in that way killed. If a 

 part of a nuclear thread could be killed in this way, the 

 externally visible consequences would certainly allow us 

 to draw conclusions on the relations of this part to the 

 hereditary characters. Perhaps an analaysis of heredity 

 can some day be made by this method, but the technique is 

 not yet sufficiently advanced for this purpose. 



However, there is another means of removing individ- 

 ual chromosomes, and this again we owe to the classical 

 investigations of Boveri. He found it in abnormal pro- 

 cesses of fertilization as they occur at times in eggs of sea- 

 urchins and star-fish, and it can be quite easily produced 

 artificially. It would lead too far from the main question 

 to go into details here. The important point for our pur- 

 pose is that, by certain interferences, a fertilization of one 

 egg with two spermatozoa can be achieved. This process 

 of dispermia leads in the nucleus of the germ, not to a 

 double, but to a triple number of chromosomes. In the 

 successive divisions the conditions become correspondingly 

 intricate, and almost any imaginable abnormal number of 

 chromosomes occurs. Nevertheless, the germs develop in 

 some cases, and then show deviations from the normal 

 type which allow a recognition of their normal relations 

 to the structure of their nuclei. Without doubt the germs 

 can, in every case, develop only those qualities the repre- 

 sentatives of which happened to be preserved in their 

 nuclei. 



We shall leave the nuclear threads, at present, and 

 return to the two pronuclei. We saw them intimately 

 combined during the entire development of the body. 

 Now the question arises as to how long this union persists. 



