CHROMOSOMES OF TIGER BEETLES 451 
reaches the prophase condition without any perceivable split in 
the chromatin threads, the diplotene stage is imperceptible and 
the diffuse condition entirely lacking. ‘The heavy, densely stain- 
ing chromatic rods of the prophase stages seem to be derived 
directly from the pachytene nucleus. The woolly chromatic 
strands of the early prophase are gradually transformed into 
more definite late prophase chromatic bars (figs. 26 to 31). The 
most marked differences, however, between the early and late 
prophase cells are the gradual increase in nuclear size and the 
development of the nucleolus from an almost non-perceptible 
body to its conspicuous and characteristic late prophase form 
(figs. 29 and 30). 
6. FIRST SPERMATOCYTE DIVISION 
A. The autosomes 
Near the close of the growth period, the cytoplasm seems to 
pass to one end of the cell, leaving the nuclear wall and the cell 
membrane almost or quite in contact, giving the cell an elongated, 
triangular appearance (figs. 29 and 30). <A single centrosome is 
sometimes seen in the central part of this cytoplasmic mass some 
distance from the nuclear wall. The large, woolly, chromatin 
rods often give indications of polarization in the vicinity of the 
appearing centrosome (fig. 29). The chromatic nucleolus now 
assumes its characteristic bivalent (but unequal) appearance of 
the first spermatocyte mitosis. Upon the appearance of the 
spindle fibers and the breaking down of the nuclear membrane, 
the cell reassumes its somewhat symmetrical form, and the 
irregular chromosomes make their appearance (fig. 31). As the 
eleven first spermatocyte chromosomes take their position on the 
metaphase spindle, they represent almost as many types as there 
are individuals, but the shape and size of each is fairly constant 
at each corresponding stage of division. Figure 37 shows in 
detail the characteristic shape of the average chromosomes at 
metaphase and the approximate point of spindle attachment. 
Spindles showing all of these elements in the same phase are 
exceedingly rare, as the shape is constantly changing with the 
JOURNAL OF MORPHOLOGY, VOL. 32, NO. 3 
