Artificial Parthenogenesis in Thalassema Mellita 133 



Fig. 48 is shown an egg in which one of the two nuclei present is 

 accompanied by two minute asters, while a single aster is seen 

 lying close to the other nucleus, evidently in preparation for a sec- 

 ond division. Fig. 49 show^s four small nuclei which have pos- 

 sibly arisen through two maturation divisions occurring internally. 

 Of course, such a condition as this might be explained as the result 

 of the formation of a tetraster without subsequent cytoplasmic 

 division, but polyasters are entirely absent in the eggs from which 

 these cases are taken, and if this were the correct interpretation, 

 some evidence of the occurrence of multipolar mitosis would cer- 

 tainly be present. It is impossible to determine whether the four 

 nuclei fuse, or not, to form a cleavage nucleus, yet that they do 

 conjugate is indicated by the fact that in later stages of the same 

 material where the cleavage amphiaster is present, a careful search 

 fails to disclose accessory nuclei outside in the cytoplasm. In a 

 few sections of the equatorial plate of the first cleavage spindle, 

 found in the same series of eggs, the number of chromosomes is 

 clearly more than twelve, although I have never counted an exact 

 multiple of that number; in Fig. 50 twenty-three chromosomes are 

 present in the section, and this would seem to prove that at least tw^o 

 of the nuclei had united. 



In a number of experiments in which it was noticed that none of 

 the eggs extruded polar bodies, besides the cases of internal ma- 

 turation already described, a still more unusual condition, which 

 may be appropriately referred to in this connection, is apparently 

 present in certain eggs. These are cases in which the first matura- 

 tion spindle is formed in the ordinary manner, but instead of 

 rotating into a radial position it becomes elongated and placed 

 symmetrically across the center of the egg. These large spindles 

 (Fig. 51), clearly showing the crosses of the tetrads and the double 

 centrosomes, predominate in the eggs of certain experiments, and 

 since later stages of the same material show many eggs divided 

 into two cells, it can hardly be doubted that they give rise to an 

 equal or nearly equal segmentation of the egg, the products of 

 which have, therefore, the value of oocytes of the second order. 

 Fig. 52 shows an anaphase of such an egg, in which the distinct 

 dyads are seen passing to the poles of the spindle. I am unable to 



