CHROMOSOME STUDIES 263 



in size. These size gradations are so dependable that one may 

 follow without difficulty any chromosome pair he chooses through 

 the cells of all of the species and genera I have so far studied. 

 If I see the whole series or, in some cases, even a part of it, I 

 can recognize a no. 6 or a no. 4, for example, as such. An idea 

 of the degree of constancy may be obtained by following any 

 chromosome through the figures from 23 to 147. In Protenor 

 belfragii Wilson ('05) was able to recognize in all cells only the 

 two largest and the two smallest pairs of chromosomes. In 

 the Tettigidae it is possible to recognize every one of the series 

 of six autosome pairs as well as the sex pair. 



In the Acrididae^ again size gradations are recognizable with 

 a considerable precision, as may be seen in the species of Steno- 

 bothrus (Meek, '12), Syrbula (Robertson, '08), Melanoplus 

 (Nowlin, '08) and numerous other genera. There may always 

 be readily recognized three small pairs and three large ones 

 with a graded series of intermediates. The sex chromosome 

 ranks from eighth to tenth in the series of twelve pairs. With 

 the exception of the three largest and three smallest pairs and 

 the sex chromosome, it is impossible to trace very definitely 

 individual chromosomes through these three subfamilies unless 

 the chromosomes happen to be in some way linked together as 

 in Chorthippus. 



Such constant size gradations recognizable in both germ and 

 somatic cells is evidence against the theory of King ('08) and 

 Haecker ('11) that size gradations are the result of unequally 

 rapid development or growth. The occurrence of these size 

 gradations in somatic cells is also an answer to Haecker's ('11) 

 criticism that such gradations have not been found outside 

 of germ cells. 



As in number and in size, so in their behavior, the members 

 of a series of chromosomes are constant to a greater or less de- 

 gree. In the Tettigidae all spermatogonial, somatic and second- 

 spermatocyte chromosomes are straight rods, pointed at the 

 proximal, and rounded at the distal end. In the prophase and 

 metaphase no rings like those in the Acrididae (Syrbula, fig. 

 157, no. 10) have thus far been found. There seems to be a 



