148 EZRA ALLEN 



Hippiscus type (McClung '14), and is explained as failure of the 

 rings to form completely, or to persist as such. Such failure 

 apparently does not occur in the white rat. The polar views 

 shown in figures 18 to 20 are to be regarded as typical in this 

 respect. 



After division takes place the movement in anaphase is rapid, 

 the small and medium-sized chromosomes aggregate close to- 

 gether quickly, but do not lose their identity until after the 

 larger ones have begun to approximate the pole. Such a well- 

 separated complex at this stage as that shown in figure 22 is 

 rather rare. On account of this rapid movement, as well as the 

 strongly convex telophase plate, study of the fate of the V's is very 

 difficult. They do not reappear as V's in interkinesis nor in the 

 second spermatocyte complexes. We ma}^ only assume that 

 their duplex constitution is retained throughout interkinesis. 



Conclusions as to the constitution of the first spermatocyte 

 euchromosomes : 



1. Whatever the shapes assumed, they are all tetrads formed 

 of four chromatids. 



2. Their organization is such that each chromatid is so related 

 to the others that it may maintain its individuality throughout 

 the various movements which occur from the beginning of dia- 

 kinesis until the separation in pairs is accomplished at anaphase. 



3. The fiber attachment is terminal, so that only single V's are 

 formed in anaphase. 



4. Ring formation is always complete, since no V-shaped 

 tetrads have been observed in metaphase conditions. 



3. The number of the first spermatocyte chroviosomes. Determi- 

 nation of the ntimber has been difficult for several reasons. The 

 chromosomes do not form flat plates, they divide non-synchro- 

 nously, the largest one {A) is frequently late in taking its place 

 on the spindle, as shown in figures 46 and 54. These facts render 

 polar views difficult to interpret. Certain false interpretations 

 are likely to arise by counting lugs separately, as in four of the 

 largest chromosomes they spread very widely. Another polar- 

 view difficulty arises from the presence of crosses. It is possible 

 so to section these that the middle parts as they lie on the spindle 

 may appear as two small chromosomes lying in the same plane. 



