230 CHARLES W. METZ 



appears now, after a careful study of these stages in a large 

 number of flies, that the so-called 'second conjugation' is of only 

 occasional occurrence, and is not a uniform stage in the chromo- 

 somal activities. In some, if not all cases, it is simply a retention 

 of the close approximation that existed in prophase. 



When considered step by step, as has just been done, it is 

 remarkable what a resemblance the above processes bear to 

 those of maturation. In the early prophase stages of either 

 somatic or gonial nuclei an almost exact simulacrum of diplo- 

 tene nuclei is often found. This extends in some cases, even 

 to definite polarization of threads within the nucleus, such as 

 is shown in figures 100 and 101.^ 



PAIRING IN DIFFERENT TISSUES AND DURING DIFFERENT 

 STAGES IN ONTOGENY 



No attempt has been made in this study to examine in detail 

 all of the somatic tissues in any one species. Various tissues 

 have been dissected out at different times, however, and fixed 

 with the gonads. In this manner I have been able to study 

 division figures in most of the tissues of the body and during 

 most stages of ontogeny. Among the organs and tissues defi- 

 nitely identified in these studies the following may be mentioned ; 

 embryonic brain, eyes, malpighian tubules and wing buds, and 

 somatic as well as germinal parts of the testes and ovaries. I 

 have also examined various bits of tissue taken at random from 

 dissected larvae and pupae of various ages. 



In addition to studying isolated pieces, I have studied sec- 

 tions of entire embryos (larvae) in which all of the tissues could 

 be examined. Of course division figures were never visible in 

 all the tissues of these total preparations, but they were fre- 

 quently found in several parts of one object.^ 



In regard to the ontogenetic development I may state that 

 I have examined all stages from the newly hatched larvae up 



* See concluding paragraph, page 257. 



' As mentioned under 'Methods' the figures in total preparations are poor, 

 but they are sufficient to show whether the chromosomes are paired or single. 



