Artificial Parihniogencsis in Thalassema Mellita 145 



vigorously at the bottom ot the dish, do not rise to the surface of 

 the water. 



9 After exposure of the eggs to acid solutions, the polar bodies 

 may continue to divide mitotically and form a morula-like cluster 

 of minute cells, thus exhibiting an attempt at parthenogenetic 

 development. 



10 In some experiments, the eggs extruded only one polar body 

 and in others neither polar body was formed. In such cases, 

 either one or both maturation mitoses take place inside the egg, 

 with the resulting formation of resting nuclei which probably fuse 

 to form a cleavage nucleus. In still other cases, there is evidence 

 for believing that the first maturation spindle may directly become 

 the first cleavage spindle, across which the egg divides into equal 

 or subequal cells. The numerical relations of the chromosomes 

 in these cases have not been definitely determined. Eggs exhibit- 

 ing these abnormalities of maturation give rise to larvae indis- 

 tinguishable from eggs which maturate normally. 



11 An endless variety of abnormal cleavages, similar to those 

 described by others, have been observed. Such cleavages lead to 

 the formation of ciliated, cellular structures which, however, 

 depart more or less widely from normal embryos. 



12 Abnormalities of mitosis, as polyasters and monasters, are 

 not infrequent, and when nuclear division is not followed by 

 cleavage of the cytoplasm, chromosomes in excess of the usual 

 number (12) may be found in a single cell. 



13 Cytasters are either absent or exceedingly rare, and cyto- 

 plasmic cleavage without preceding nuclear division has not been 

 observed. 



14 Amoeboid movements of the egg are rare, and when they 

 occur, are not extensive; "fusion phenomena" are lacking. 



15 Cell division would seem to be a fundamental and essential 

 factor in differentiation, since in no instance was a differentiated, 

 ciliated structure observed which was unsegmented; the partheno- 

 genetic pseudo-trochophores, which have been described for 

 Chaeptopterus and other annelids, are entirely absent. 



Zoological Laboratory 



University of Missouri 



August 15, 1906 



