132 George Lejevre 



show different stages of the first cleavage mitosis. If my inter- 

 pretation of these conditions is correct, the case is identical with 

 the rarer type of parthenogenesis described by Brauer ('93) for 

 Artemia, where the chromosomes of the second polar body are 

 retained by the egg and give rise to a reticular nucleus, as earlier 

 described by Boveri ('87) in Ascaris, which acts like a sperm nucleus 

 and conjugates with the nucleus of the egg. Brauer's observa- 

 tions apparently confirmed Boveri's conception that "Partheno- 

 genesis is the result of fertilization by the second polar body" (/.c, 

 p. J^). Of course, if the fusion of the two nuclei takes place, one 

 would expect to find 24 chromosomes in the equatorial plate of 

 the first cleavage spindle, but unfortunately I have not been able 

 to obtain a favorable section in which the number of chromosomes 

 could be accurately determined, but there are clear indications 

 that it is greater than 12. The difficulty in establishing this point 

 is not surprising, as the material from this experiment, which was 

 preserved for the later stages, was quite limited in amount. 



h Absence of both Polar Bodies 



A more frequent abnormality is found in the failure to extrude 

 both polar bodies, yet eggs which show this peculiarity may develop 

 into swimming larvae. The condition was observed in a num- 

 ber of experiments when after careful search not an egg was seen 

 to give off the polar bodies, but the percentage of developing eggs 

 in such cases was as high as the average. Fig. 47 shows a sub- 

 merged first maturation mitosis in a late anaphase; the centro- 

 somes are clearly seen to be double and the chromosomes are in 

 the form of dyads and not single rods. It is exceedingly difficult 

 to reconstruct the successive stages in the internal maturation of 

 such eggs, and here again positive proof cannot be furnished. 

 Two resting nuclei are undoubtedly formed, as they occur in 

 many eggs, but I am inclined to believe that these usually fuse at 

 once to form a cleavage nucleus without the occurrence of a second 

 maturation mitosis. Although I have not succeeded in finding a 

 complete series of stages, there is some evidence, however, that 

 in rarer cases the two nuclei just referred to may divide again mitot- 

 ically, with the resulting formation of four smaller nuclei. In 



