710 C. E. McCLUNG 



The movements of the chromatids, the relation of the spindle 

 fibers to the chromosomes and the form of the anaphase chromo- 

 somes is similar to those of the rods and V's, so need not be con- 

 sidered here. The important matter in connection with the 

 crosses is to understand that they represent a mid-stage in the 

 movement of the chromatids, either in prophase or in metaphase. 



4. Ring-shaped tetrads. If confusion exist in reports of the 

 prophase condition of the rings, it is certainly multiplied when 

 attempts are made to describe the metaphase forms. Here are 

 added a number of factors which complicate the problem, but 

 which yet give meaning to the chromosomes and to their move- 

 ments. We approach an analysis of the metaphase conditions 

 fortified by a reasonably strong consensus of opinion regarding 

 (1) the relations of the chromosomes of this period to those of 

 the spermatogonium, and (2) concerning the inner structure of 

 the tetrads. Also (3) these are traced into the metaphase, where 

 we have to note (4) their position in the mitotic figure, (5) the 

 movements of the parts, (6) their relation to the archoplasmic 

 fibers, (7) their character after separation. These will first be 

 discussed for the Hippiscus type of rings and then for the Steno- 

 bothrus type. 



(1) It is now universally admitted that the chromosomes of 

 the first spermatocyte are made up of four chromatids, and a large 

 number of cytologists beheve that two of these are of maternal 

 and two of paternal origin from the homologous pair of spermato- 

 gonial chromosomes. In the rings (2) they are so disposed that 

 the maternal pair constitute one-half the periphery of the ring, 

 the paternal pair the other, with the direction of the longitudinal 

 cleavage passing through the arms of the ring parallel to the 

 plane in which they lie, so as to produce two superimposed rings, 

 alike in their derivation. (3) The metaphase sees these same 

 forms placed in the mitotic figure where (4) they lie as rings ex- 

 tended in the equatorial plate, so that they are visible from the 

 pole of the spindle. In most cases they lie perfectly flat in this 

 plane so that the entire ring is sharply in focus at one time, with 

 the exception of the synaptic extension, first seen in the prophase, 

 which now lies at a point nearest the axis of the spindle and 



