80 bulletin: museum of comparative zoology. 



Figure 58 (Plate 5) shows the element during the zygotene stages — 

 as indicated by the incompletely conjugated pair of threads near the 

 middle of the figure — in a condition of complete parallel association 

 for the two conjugants, but a condition in which the members of the 

 pairs of granules, the chromomeres, are distinct. A close examination 

 of this spireme of B discloses a series of cliromomeres in addition to, 

 and smaller than, the three already mentioned as characterizing the 

 element. 



For convenience in description the more prominent granules or 

 chromomeres will be given separate designations. The five granules 

 which I wish to mention more particularly will be numbered in order 

 from the proximal (no. 1) to the distal end (no. 5, figure 58). I shall 

 also call attention to the two paii's of small granules between numbers 

 3 and 4 and to the two pairs of still smaller ones between 2 and 3. I 

 should not omit to direct attention to the series of granules between 

 numbers 1 and 2 and between numbers 4 and 5, but detailed considera- 

 tion' of those already mentioned will probably suffice for the purpose 

 in view. 



I was at first impressed by the constancy in relative size and posi- 

 tion with which some of these granules recurred in different examples 

 of B and at different stages in a single individual (no. 772). It then 

 occurred to me to compare the same element at about the same stage 

 for all the thirteen animals from which material was available. Figure 

 97 (Plate 8) is the result, each of the separate draAvings having been 

 taken from a different animal. The constancy with which the minute 

 details of size and arrangement of the parts of this pair were repeated 

 in all of the individuals was surprising. Not only are the five more 

 prominent chromomeres repeated in approximately the same relative 

 sizes and positions, — as shown in figure 97, where corresponding 

 granules are connected by dotted lines, — but there is likewise a strik- 

 ing correspondence in the more minute details. For example, the 

 segment between the granules numbered 3 and 4 always contains two 

 pairs of granules of about the same relative size, though they vary 

 somewhat in relative position. On the other hand, the segment be- 

 tween 2 and 3 is characterized by the entire absence of any prominent 

 granules. In some cases, however, as in/, i, and k, figure 97, granules 

 can be made out in this segment, and when this is possible there are 

 always two pairs of very small ones in the same relative positions. 



It is true that there are some variations in the appearances of the 

 segments between granules numbered 1 and 2 and between 4 and 5, 

 as well as differences in the actual size of the numbered granules. 



