104 N. M. Stevens 



proving that the heterochromosome is not divided in this mitosis 

 and that the spermatozoa are dimorphic, half of them containing 

 ten, the other half nine chromosomes. 



The chromosomes of an egg follicle cell are shov^n in Fig. 21, 

 and those of a spermatogonium in Fig. 22. The synizesis and 

 synapsis stages are quite different from those of Photinus penn- 

 sylvanicus, and similar to those of Ellychnia. The synizesis stage 

 has the short crowded loops (Fig. 23). The synapsis stage is less 

 distinct than in some of the cases previously described. One occa- 

 sionally finds a nucleus with the longer synaptic loops (Fig. 24), 

 but more often synapsis and union of chromosomes occur at the 

 same time, giving a mixture of loops, and spireme with sharp 

 angles of which Fig. 25 is perhaps a fair specimen. The hetero- 

 chromosome may be seen in this stage but is more conspicuous in 

 the later pale spireme stage (Fig. 26). 



Fig. 27 is the first spermatocyte equatorial plate. Fig. 28 and 

 Fig. 29 the metaphase and anaphase, showing the unpaired chro- 

 mosome dividing late. In fact, it frequently divides so late that 

 the two daughter-heterochromosomes are still quite close together 

 and connected by linin fibers in the metaphase of the pairs of 

 second spermatocytes, as shown in Figs. 30 and 31. A pair of 

 daughter plates are given in Fig. 32, showing that as in P. pennsyl- 

 vanicus, the heterochromosome does not divide in the second 

 spermatocyte. Usually it lags behind the daughter plate to which 

 it belongs, so that the two anaphases (Figs. 29 and 33) are charac- 

 terized by a pair of daughter heterochromosomes, and by a single 

 heterochromosome, respectively. 



These two species of Lampyridae are the only cases which have 

 been found, where the unpaired heterochromosome divides in the 

 first spermatocyte instead of the second. In one, Photinus con- 

 sanguineus, it divides very late, in a stage which is a late anaphase 

 or telophase for the other chromosomes, while in the other species, 

 P. pennsylvanicus, it divides at the same time with the other 

 chromosomes, or only slightly later. It will be interesting to 

 study the spermatogenesis of other Lampyridae for comparison 

 on this point. An abundance of adult material of several other 

 species has been secured and examined, but only spermatozoa 



