42 STUDIES IN SPERM ATOGENESIS. 



Doryphora decemlineata (Family Chrysomelidae). 



Doryphora decemlineata has been the most difficult one of the collec- 

 tion to work out satisfactorily. The chromosomes in the spermato- 

 gonial plates were in most cases much tangled, and the behavior of the 

 heterochromosome pair was such as to suggest an ' ' accessory chro- 

 mosome" rather than an unequal pair. Abundant material for the 

 study of somatic cells was at hand, but nothing favorable could be 

 found in the sections. 



Two spermatogonial plates, containing 36 chromosomes, are shown 

 in figures 151 and 152 (plate xn). The small heterochromosome (s) is 

 slightly elongated. The synizesis and synapsis stages are especially 

 clear. The chromosomes, after the last spermatogonial mitosis go 

 over immediately into a synizesis stage consisting of a polarized group 

 of short loops, which later straighten and unite in pairs (figs. 153 

 and 154). From these loops are formed the spireme (figs. 155-158), 

 which splits and segments, producing various cross, dumb-bell, and 

 ring forms (figs. 159-163). As in most of the other species of 

 Coleoptera, the unequal pair is not distinguishable until the spireme 

 stage. Figure 162 is an unusual prophase in which all of the equal 

 pairs show a longitudinal split as well as a transverse constriction, 

 and the larger heterochromosome (/) is also split. Figure 163 shows 

 a somewhat later and more common prophase in which the unequal 

 pair, one ring, crosses, and dumb-bells may be seen. This figure, as 

 well as figures 164-168, show the unequal pair in various relations to 

 the other chromosomes. This pair in Doryphora consists of a large 

 V-shaped chromosome with a small spherical one attached to it in 

 different positions. When the small one is behind the V, the group 

 has the appearance of an orthopteran " accessory." 



Figures 169-171 show the separation of the two elements outside of 

 the equatorial plate, while in figure 168 the unequal pair is in line 

 with the other chromosomes. In figure 172, an anaphase, the unequal 

 elements are barely separated, while the metakinesis of the other pairs 

 is much further advanced. 



Figures 173 and 174 are equatorial plates of the first division, one 

 showing only the larger element of the heterochromosome pair (fig. 

 174, x), the other both elements (fig. 173, / and s). In the late 

 anaphase (fig. 175) the larger heterochromosome is often seen outside 

 of the polar mass, reminding one again of the "accessory" in the 

 Orthoptera. Occasionally it is found in some other isolated position 

 (fig. 176). Equatorial plates of the second division show the same 

 conditions as in the other species; some contain the larger hetero- 

 chromosome, others the smaller one (fig. 177, a and ). It was impos- 



