Dr. C A. Kofoiil on PlooiltMina illinoiaeiitjis. 



U!» 



In Stephanosphwra tliii pDlarity in structure is hut slightly 

 inarktHl in the coUiny, hoing iiuUcatcil in some colonies hy 

 the asynmietrical position of the cells, hut there is a physio- 

 logical differentiation in that one pole of the colony leads in 

 locomotion. In this genus also, according to Cohn (1852), 

 the rotation is in either of the two directions and is subject 

 to Irequent change. No predominant direction was noted 

 hy him. 



in I'andoiina the only structural exitression (jf polarity is 

 found in the greater development of the stigmata in the cells 

 in the anterior end of the colony. In other jiarticulars the 

 poles are not differentiated. Braun (1851) maintains that in 

 this geims the rotation is constantly around the long axis of 

 the colony in the direction of the hands of a clock, when the 

 motion is toward the observer. Niigeli {Jide Hiitschli, 1883- 

 1887, p. 858), on the other hand, observed rotation in both 

 directions. My own observations upon Pandorina jtiorum 

 show beyond question that the direction of rotation is not 

 constant, us the following table demonstrates: — 



The table gives the direction and number of changes in 

 direction in rotation of ten colonies, each observed for one 

 minute. The plus and minus signs indicate the estimated 

 preJouiinance in duration. According to the table the in- 

 stances of direction observed are approximately equal for the 

 two directions, though that from right over to left showed 

 the greater duration. The younger and smaller colonies 

 showed much the greatest activity and exhibited more 

 trequent changes in direction than the older colonies. In all 

 observed cases the same end continues to lead in locomotion, 

 physiological polarity being thus fully developed in this genus. 



In the case of h'udon'na the structural polarity of the 

 vegetative colonies is no more marked than it is in Pandorina^ 

 though according to Carter (1858) there is in the monoecious 

 sexual colony a differentiation, in that the four cells at one 

 [>ole divide to form spermatozoa, while the remaining twenty- 

 eight become egg-cells, it should be noted in this connection 

 that no such colonics were observed by Cioroschankin (1875) 

 in the sexual generation. The literature at hand presents no 



