GERM CELLS IN PEDICELLINA AMERICANA 13 



where the parallel bivalents have united at both their ends to 

 form a much elongated ring. In Fig. 24 all the chromosomes 

 have opened and the bivalent arms twine around each other 

 several times. Finally Fig. 25 represents a somewhat later 

 stage in which nearly all the chromosomes are in the form of 

 elongated rings. In other cells, the elongated rings may be 

 less frequent (Fig. 26), their place being taken by the bars. 

 These represent the sister bivalents which have not opened out 

 to form a ring after the increase of the angle of the primary 

 V's, but have rather come into more intimate relations with 



(X. 



jy.^WJ'yA y'y/ 



c d e f g 



Text-fk;. I. 

 Diagram of chromatic transformations from synapsis («) to the first maturation 

 division (^). 



each other. It is important to observe that these bars are, at 

 this stage, about twice as thick as the elongated rings, show- 

 ing that they are double. What is more convincing, however, 

 is the fact that in some cases the longitudinal split may actually 

 be traced throughout their length. At the same time, the 

 chromosomes have considerably concentrated, so that the 

 changes within the nucleus can now be more easily determined. 



From this point onward, the main changes consist in the 

 further concentration of the elongated figures into more perfect 

 rings and thickened double bars. Thus, as in Fig. 27, these 

 two main types, now staining intensely, are found side by side, 

 the double bars, present in the larger number, showing charac- 

 teristic bendings into thick U-shaped figures. 



The spermatocytes are now at the end of the growth period, 

 and the eleven chromosomes distributed around the periphery 



