ASSOCIATION OF CHROMOSOMES IN DIPTERA 231 



to the sexually mature fly in several species of Drosophilidae, 

 Muscidae and Anthomyidae. 



The results of all these studies on somatic tissues may be 

 summed up in one sentence, namely, that in all tissues of the 

 body and during all stages in development from the newly 

 hatched larva to the adult fly the paired association of corre- 

 sponding chromosomes is a universal characteristic. So far 

 as I have been able to determine, the pairing phenomena are 

 identical in all diploid cells, whether somatic, spermatogonial 

 or oogonial, from the egg to the adult. 



DIFFERENT SPECIES AND FAMILIES COMPARED 



In order to determine whether the paired association of chromo- 

 somes is characteristic of all Diptera or whether it is restricted 

 to certain individuals or groups, an attempt has been made 

 to study representatives of all the principal divisions in the 

 order. As a result, sixteen families ranging from among the 

 lowest to the highest have been included in the survey. Some 

 of these families are represented by one or two species, others 

 by several species. Since the principal aspects of the pairing 

 phenomena are essentially the same in all of the flies studied 

 no attempt will be made to treat each individual species. In- 

 stead, a few characteristic members will be chosen as repre- 

 sentatives of the respective families. Likewise, no attempt 

 will be made to give a complete account of the chromosome 

 behavior in each species treated. In many cases only enough 

 figures are reproduced to show the nature of the chromosomes 

 and their paired association. 



For convenience the order of treatment of the families is the 

 reverse of that given in the synopsis (i.e., from the highest to 

 lowest instead of vice versa), except that the Muscidae will be 

 considered before the Sarcophagidae. 



Muscidae 



Calliphora erythrocephala (figs. 51-66). Figures 51 and 52 

 represent the haploid group of this species, taken from first 

 spermatocyte divisions. The group consists of four similar, 



