THE CHROMOSOMES 111 



cytoplasm does not here affect the character of the 

 larvae, it is rational to suppose that an increase such 

 as is present in the giant eggs likewise produces no 

 such effects as observed in the larvse. At the same 

 time, normal eggs were cross fertilized and in the 

 two-cell stage the blastomeres were separated. The 

 contributions by the two parents were relatively the 

 sam^e as in the normal egg. These larvse were like 

 those from egg fragments, and serve as a control of 

 those larvse in so far as they bear on the question of 

 how far size alone may affect the result. Moreover, 

 in them, the relation of the chromosomes to the 

 cytoplasm is the same as in the normal egg (whether 

 the sperm does or does not bring in cytoplasm). 

 Hence, since the amount of cytoplasm is shown to 

 have no influence on the character of these larvse, 

 there is no reason for supposing that it had any 

 influence in the case of the giant eggs. 



Boveri's studies upon dispermic fertilization of 

 the egg of the sea urchin bear directly upon the 

 question at issue. He found that when two sperm 

 simultaneously enter the same egg, each brings in a 

 centrosome, so that a tetra- or tri-polar spindle is 

 formed for the first division, as shown in Fig. 37. 

 Instead of a double set of chromosomes, as in normal 

 fertilization, there are three sets. At the first 

 division, the chromosomes^ are irregularly distrib- 

 uted upon the multipolar spindles. In consequence, 

 some cells may get one of each kind of chromosome, 

 while other cells may get less than a full complement 

 (Fig. 38). These dispermic eggs almost always give 



