234 MICHAEL F. GUYER. 



Fig. in shows a late metaphase in which the special element 

 is dividing lengthwise. Figs. 112, 114 and 117 illustrate various 

 cases in which division is in progress or has occurred. 



From time to time an especially bothersome element appeared 

 in some cells which complicated the interpretation of conditions 

 in the tissue of females. It took the form of an elongated rod 

 which occurred along with the curved element. Like the curved 

 element, it often was of lighter staining capacity and had the 

 former not been distinctly visible as a separate body the second 

 element might have been mistaken for it. Whether or not it 

 consists of several of the ordinary chromosomes which have 

 remained attached and are dividing as one body is not wholly 

 clear. This seems to be the most plausible interpretation 

 although it is not apparent why such a mass should stain less 

 deeply. That such compounding does occur occasionally in the 

 cells of various vertebrates, I am strongly inclined to believe, 

 from the evidence I have seen of variations in the number and 

 size of chromosomes in other avian and mammalian tissues. 

 Apparently chromosomes in such cases represent congeries of 

 units of a lesser order which may be done up in fewer and larger, 

 or more numerous and smaller packets, contingent upon as yet 

 unknown conditions of equilibria in the cells. This probability 

 constantly hangs over the student of these forms as the chief 

 one which is likely to vitiate his conclusions. All the corrective 

 he has is to make great numbers of observations and base his 

 conclusions upon the conditions which he finds strongly pre- 

 ponderant. 



Figs. 101 and 102 are drawings made from dividing cells in 

 a five-day chick. While sex cannot be determined from macro- 

 scopic evidence, or even microscopic examination of the in- 

 different gonads at this early date, from the fact that the cells 

 each contain but a single large curved element the inference 

 would be that the embryo bearing these cells is a female. In this 

 connection, the writer was greatly interested in Fig. 2 of a recent 

 paper by Swift ('15). The figure shows a section through the 

 indifferent gonad of a four-day chick embryo and includes a 

 division figure of a primordial germ-cell. Although Swift's 

 study was not on chromosomes and he does not mention the 



