A\ enrich: spermatogenesis of PHRYNOTETTIX MAGNUS. 107 



include under the term "V-shaped" all the chromosomes which have 

 a non-terminal spindle-fiber attachment. They may be regarded as 

 rods which have become bent at the point of the spindle-fiber attach- 

 ment. Broadly, therefore, we may look upon all cliromosomes as 

 rod-shaped, but it will make description easier to distinguish the 

 types just mentioned. 



In attempting to show that chromosomes have a constant size and 

 shape for each species, as well as a constant number, it will be well to 

 call attention to the fact, so clearly stated by McClung ('14), that the 

 point of the spindle-fiber attachment is, as a general rule, constant 

 and therefore one of the indications of a persistent organization for 

 each individual chromosome. 



Some groups of animals exhibit a high degree of uniformity in the 

 shape and size of the chromosomes in any species, as for example, 

 among the Crustacea and the Amphibia, while others show a great 

 variety of forms (Orthoptera, mammals). In the groups with diverse 

 shapes and sizes of chromosomes, the striking fact was pointed out by 

 Montgomery ('01) that there are two of each different size. Mont- 

 gomery reached the logical conclusion that of the two equivalent 

 series existing in «ach cell, one had been derived from the maternal 

 and the other from the paternal ancestor. 



That the same series of sizes and shapes reappears in each cell- 

 generation, is recorded by nearly every observer whose material is 

 favorable enough to admit of such comparisons. The work of Mc- 

 Clung ('00, '02, '04, '08b, '14), Sutton ('02, '03), Baumgartner ('04), 

 Nowlin ('08), Pinney ('08), Robertson ('08) on orthopteran material 

 has done much to establish this fundamental feature of individuality. 

 A very interesting series of observations on this point is that of Meek 

 ('12a, '12b) on Stenobothrus. He describes the results of a series of 

 careful measurements of cliromosome-dimensions in diiTerent genera- " 

 tions of cells, and as a result of these observations becomes convinced 

 of the existence of persistent individuality. I may quote some of his 

 conclusions ('12a, p. 24, ff.): — " (1) In all metaphases the relative 

 positions of the chromosomes in the equatorial plate appear to be 

 arbitrary. (2) The rods composing all ordinary chromosomes are 

 cylindrical with rounded ends, and of an unifonn and constant diame- 

 ter, viz., 0.83 micra. In each species eight lengths have been found, 

 and these constitute members of a series in arithmetical progi'ession, 

 of which the difference between consecutive terms is equal to the 

 radius of the rod. The heterotropic chromosome does not belong to 

 this general series, for, although equal in length to the longest rod, its 



