Io6 A^. M. Stevens 



chromosome {x) frequently divides somewhat later than the others. 

 Polar plates of the two classes of second spermatocyte mitoses are 

 shown in Figs. 47 and 48. So far as investigated the Elateridae 

 have an unpaired heterochromosome which differs from that of 

 the Lampyridae in dividing in the second spermatocytes. 



NECROPHORUS SAYI (fAM. SILPHIDte) 



Necrophorus sayi has an unpaired heterochromosome, while 

 Silpha americana ('06, PI. XI, Figs. 141-150) has an unequal 

 pair of heterochromosomes. Necrophorus also differs from Sil- 

 pha in having a much smaller number of chromosomes, thirteen 

 in the spermatogonia (Fig. 49), while Silpha has forty. The 

 synizesis stage is of the finely wound spireme type with the odd 

 chromosome usually visible. There is no preliminary stage that can 

 be pointed out as a synapsis stage, but as the chromosomes remain 

 united in a spireme up to the prophase of the first maturation 

 division, when they appear in the reduced number, it seems certain 

 that synapsis must occur at the close of the last spermatogonial 

 division before the synizesis stage. The bivalents of the prophase 

 of the first spermatocyte mitosis (Fig. 50) have the appearance of 

 two spermatogonial chromosomes united end to end, and in the 

 spindle they are merely somewhat shortened (Fig. 52). 



The first spermatocyte has seven chromosomes with the unival- 

 ent one oftenest at the center of the group (Fig. 51). Fig. 52 shows 

 the seven chromosomes of one spindle drawn at three different levels 

 of the same section. Here the odd chromosome is at the periphery 

 of the plate. The centrosomes in this form are very large. Polar 

 plates of one spindle are shown in Fig. 53, and in Fig. 54 equa- 

 torial plates of the second divisions which proceed as in other sim- 

 ilar cases giving the usual dimorphic spermatids, containing in 

 Necrophorus six and seven chromosomes. 



CHRYSOMELA SIMILIS (fAM. CHRYSOMELID^) 



Most of the Chrysomelidae have an unequal pair of hetero- 

 chromosomes, but Chrysomela similis, like the Diabroticas, has 

 an odd chromosome. At the close of the synizesis stage this 



