366 THEOPHILUS S. PAINTER 



One very constant feature of the eggs showing a tetraster is 

 the occurence of a protoplasmic ball which lies on the blasto- 

 mere showing this condition. There seems to be an intimate 

 connection between the formation of the ball and the failure 

 of the egg to divide. This point will be touched upon again. 



The abnormal positions which the A and B blastomeres take up 

 is to be traced, in part at least, back to the 3-cell stage, when the 

 A and B cells separated (fig. 1). It is probable, however, that this 

 is not the only source of the abnormality, for not infrequently, one 

 finds eggs like those shown in text figure N. As may be seen in 

 the figure, the A and B cell lie pressed against each other, and 

 are dividing. The interesting thing is that the Po cell, is dividing 

 in an abnormal plane. This condition could come about only in 

 one of two ways. Either there has been a rolling or shifting of 

 some of the cells, or, their polarity has been changed. Of the two 

 possibilities the former seems the most probable since in the 

 normal egg, a shifting process is involved which brings the B and 

 Po blastomeres together (compare with figs. F and G). As we 

 know nothing definite about the cause of the shifting in the normal 

 egg, it is useless to speculate over the matter at this time. It 

 seems worth while, however, to point out that the separation 

 of the A and B cell might come about by an increase of surface 

 tension. These cells normally lie pressed against each other, but 

 were the surface tension of them increased, as through some 

 action of the CO2, then they would separate. If the Pi cell were 

 also affected, the effect (that is, the separation) might be still 

 more marked. 



Before we take up the relation between the abnormalities found 

 in cleavage and those exhibited by the fully developed worms, 

 it will be necessary to describe a few of the more striking points 

 in Ascaris development. Thanks to the works of Boveri ('99) 

 and Zur Strassen ('96), we know the origin and fate of practically 

 every cell in the young worm. 



A few schematic sketches of the normal development are given 

 in figures E to I. The first division results in two blastomeres. 

 Si and Pi respectively, following Boveri's nomenclature. These 

 two cells have different potentialities. In the next division 



