454 ^' ^' Stevens 



bling in this respect theLampyridae and Elateridae aswell as many 

 of the Orthoptera and Hemiptera. 



In the spermatogonia! equatorial plate of Diabrotica vittata, 

 we find 21 chromosomes (PI. I, Fig. i) of various sizes and shapes. 

 If X be considered the heterochromosome, the others can be mated, 

 forming ten equal pairs. In sections stained with iron haematoxy- 

 lin the division of the testis into several definite regions is very 

 striking. The resting spermatogonia hold little of the stain, 

 while the chromatin of the spermatocytes in synizesis and synapsis 

 stages is very black, and again the spireme stage is pale. The 

 synizesis stage here, as in several other Coleoptera (Stevens '06), 

 appears to be a prolonged telophase of the last spermatogonia! 

 mitosis. Fig. 2 shows the appearance of the short, crowded 

 chromatin loops in synizesis. Following this stage comes a period 

 in which the chromosomes are uniting in synapsis, and one finds 

 many nuclei similar to Fig. 3, some of the loops still short as in 

 Fig. 2, others longer and showing a sharp angle or a knob at the 

 point of union of two chromosomes. There is no such definite 

 bouquet stage as in many forms, but one next finds a stage in which 

 there are irregularly disposed loops with many free ends and some 

 sharp angles like those in Fig. 3 (Fig. 4). In this stage the hetero- 

 chromosome (x) is for the first time evident, condensed against 

 the nuclear membrane. This stage rapidly goes over into the 

 spireme stage (Fig. 5), where all of the chromosomes except the 

 heterochromosome (x) seem to be united into a single spireme 

 thread, and the points of union are no longer visible. The spireme 

 is very pale and the heterochromosome therefore very conspicuous. 

 There is nothing unusual in the prophases of the first division. 

 The spireme segments and splits longitudinally, the daughter 

 elements separate as in Fig. 6, then unite again and form rods, 

 dumb-bells, V's and rings (Fig. 7). The chromosomes in the 

 spindle (Fig. 8) are so attached to the spindle fibers that in meta- 

 kinesis they separate into their univalent components, and go to 

 the poles as short thick V's which mass together but soon separate 

 for the second division without any definite rest stage. The 

 unpaired heterochromosome {x) is of course connected with only 

 one pole of the spindle and does not divide in this division. Fig. 



