Artificial Parthenogenesis in Thalassema Mellita 131 



until it comes to lie much nearer the center of the egg. In this 

 unusual situation, it completes the mitosis and gives rise, without 

 much doubt, to two resting nuclei. Fig. 45 shows a fortunate 

 section in which the first polar body is present and the second 

 spindle lies deep within the egg; the chromosomes which are single 

 rods are in a late anaphase and have alreadyreached the poles. The 

 spindle, which is cut throughout its entire length, as both centro- 

 somes are present in the section, is perfectly normal in all re- 

 spects save its position and unusual length. The objection can- 

 not be made that this might be the cleavage spindle, as the two 

 are entirely different in appearance. Although the proper sequence 

 of stages cannot be determined with absolute certainty from a 

 study of the preserved material, there can be little doubt that this 

 particular mitosis, and many others like it which I have seen, is 

 taking place inside the egg. All of the eggs on which I have based 

 this conclusion belong to a single experiment, No. 29 of my notes, 

 in which not an instance of the formation of the second polar body 

 was observed while the eggs were alive; sample lots from this 

 experiment were killed at intervals during the maturation period, 

 and I have sectioned several stages of the series. My attention 

 being attracted to the peculiarities of maturation at the time of 

 the experiments, I was especially careful to make detailed notes 

 of each case and to look over a large number of living eggs which 

 show^ed unusual conditions. From the data given in my notes I 

 feel confident that none of the eggs of experiment No. 29 extruded 

 the second polar body, and it is quite unlikely that the spindle 

 shown in Fig. 45, which is one of many similar cases found in the 

 same material, would have later assumed a normal position and 

 thrown off the polar body. Although I have not found all the 

 intermediate stages, numerous cases like Fig. 46 occur in the same 

 series of eggs, and it would seem highly probable that the two 

 nuclei present are the result of the submerged mitosis and repre- 

 sent the egg nucleus and the nucleus of the second polar body. 

 In spite of the absence of indisputable proof, there can be little 

 doubt that the two nuclei fuse to form a cleavage 'nucleus, since in 

 later stages of the series many eggs are found which contain a single 

 large nucleus accompanied by two asters, while still other eggs 



