530 ' CLAEENCE E. McCLUNG 



both extremities and, until it appeared, I was inclined to believe 

 that the unipolar union, rather common in the case of tetrads 

 nine and ten, was lacking and that some modification of the 

 association force existed. It is now evident that the conditions 

 are essentially the same in both cases, except that the more 

 frequent occurrence of the large ring and its complete char- 

 acter would suggest a longer history of multiple constitution. 



III. CHROMOSOME CONDITIONS IN THE GENUS MERMIRIA 



At the time of my first report ('05) upon Mermiria I had 

 studied aU the available Acrididaean species and, in every indi- 

 vidual, found, only one type of chromosome — a telomitic rod in 

 the spermatogonium, which, after synapsis with its mate, ap- 

 peared in the form of a Hippiscus-type ring or in some modifi- 

 cation of the type. Although familiar with the atelomitic form 

 of chromosomes in other material, I had never seen it in the 

 Orthoptera and had no reason to suspect its occasional appear- 

 ance. Failure to consider the possibility of such chromosome 

 forms was responsible for my misinterpretation of the multiple 

 chromosomes in Mermiria, through which I made the serious 

 error of reporting the segregation of whole tetrads. Although, 

 with increased knowledge of the conditions in the group, it is 

 now possible to determine with certainty the nature of the mul- 

 tiple chromosomes, at the time of my first acquaintance with the 

 phenomenon of chromosome combinations the constancy of 

 chromosome structure and behavior was so marked as to make 

 quite unjustifiable any assumption of variation. Added to this 

 is the fact, which seemed at the time very significant and which 

 even yet is not satisfactorily explainable, that in certain indi- 

 viduals the multiple has a series of definite constrictions corre- 

 sponding in number and position to what would exist in a decad 

 element. Finally; actual separation in the first spermatocyte 

 metaphase at the level of these constrictions in certain cells per- 

 suaded me of their value as an indication of chromosome bound- 

 aries. The theoretical difficulties involved in explaining the 

 preservation of the complex on the assumption of tetrad segre- 

 gation finally convinced me that I was probably mistaken, but 



