558 CLARENCE E. McCLUNG 



4. Chroinosome forms 



In a previous paper ('14) I have considered at length the 

 subject of chromosome forms in the Orthoptera and do not here 

 desire to go into the subject beyond what is necessary to an 

 understanding of the multiples. A glance at plate 2 will show 

 how strongly these elements differ from the tetrads in metaphase. 

 The typical Orthopteran chromosome is telomitic and, in polar 

 views of the spermatogonium and second spermatocyte meta- 

 phase, it appears as an approximately straight rod which, in 

 the anaphase, becomes divided into daughter rods of similar 

 nature. In the first spermatocyte these rods, joined in pairs to 

 form tetrads, show a great variety of shapes in metaphase, but 

 in the anaphase again become reduced to the form of two rods 

 joined at one end to form a simple V, the enclosed space of which 

 lies between two chi'omatids of the former tetrad. Upon divi- 

 sion of the hexad in the first spermatocyte of Hesperotettix this 

 condition is again reahzed for the rod-portion, but opposite this 

 in the other anaphase group stands a V, the arms of which are not 

 simple rods but double ones, and the enclosed space of this lies, 

 not between chromatids, but between whole chromosomes. The 

 nature of this double-V I have considered fully in former papers. 

 Its peculiarity of form is due to the fact that fiber attachment is 

 non-terminal — a condition resulting from the union of non- 

 homologous chromosomes and not from a real shift of the fiber. 

 AU this is very clear in Hesperotettix, and the character of the 

 double V is beyond question and easy of determination. From 

 this one would be inclined to generalize and to say that where 

 fiber attachment is shifted from the termhial position, producing 

 double V's in the first spermatocyte anaphase, it is due to the 

 union of non-homologous chromosomes. Of course to make this a 

 valid argument there would have to be a corresponding reduction 

 in the group number of free elements. This condition is fully 

 met in Hesperotettix and is confirmed by the differential mor- 

 phological characters of the elements involved. In the absence 

 of such criteria based upon structure, the sole test regarding 

 the character of the double V's would be that of numerical 

 conformity. 



