ASSOCIATION OF CHROMOSOMES IN DIPTERA 235 



Ravinia peniculata (figs. 98, 99). This species is indis- 

 tinguishable from those of Sarcophaga in respect to pairing 

 phenomena. Figures 98 and 99 are ovarian (early pupal) 

 metaphases showing the six pairs of chromosomes essentially 

 like those of Sarcophaga. The latter shows the metaphase 

 splitting of the chromosomes very clearly (compare with figure 

 77). 



Anthomyidae 



Homalomya sp. (figs. 100-105). Particularly clear prophase 

 figures have been secured in this species, both with respect 

 to somatic and to spermatocyte divisions. The chromosome 

 group is practically indistinguishable from that of Calliphora 

 (figs. 51-57). Figures 100 and 101 are very early prophases 

 from somatic nuclei, illustrating the configuration of the chromat- 

 ic threads at this time. The former is from an entire, or almost 

 entire nucleus, in which the bivalent (double), long drawn out 

 threads, each representing a pair of chromosomes, are discern- 

 ible. Attention is particularly called to the polarization of 

 these threads and the resulting similarity in appearance between 

 this somatic prophase and the synaptic stages accompanying 

 maturation in many other animals. Figure 101 represents a 

 similar stage from the same tissue, but includes only a portion 

 of the nucleus. A later stage in which these threads lose their 

 polarity and contract before giving rise to the metaphase chromo- 

 some pairs is shown in figure 102. In comparison with such 

 somatic and sperm atogonial prophases it is of interest to exam- 

 ine corresponding stages in the maturation divisions. Figure 

 103 is a. portion of a second spermatocyte prophase and shows 

 sister chromosomes closely intertwdned preparatory to going 

 on the spindle. In rnetaphase (fig. 104) they come to lie one 

 above the other in the equatorial plane. Figure 105 is a second 

 spermatocyte anaphase. In figure 103 only three of the chromo- 

 somes are represented, but in 104 and 105 the full (haploid) comple- 

 ment is present. The double elements in these cases are split 

 univalten chromosomes, the two members of which separate 

 in anaphase as shown in figures 104 and 105. It is important 



