Genie Control of Development 297 



bundle. Actually, both the visible behavior in the Balbiani rings of 

 Chironomus, where the bundles separate into fibrils varying to sub- 

 microscopic size (Bauer, Beermann), as well as the calculation from 

 DNA quantity (Kurnick and Herskowitz), which also leads into the 

 submicroscopic field, show that we cannot call this a bundle of 

 chromosomes, that is, a polyploid structure as in the cases mentioned 

 above. Undoubtedly, there are only four chromatids, which may be 

 separated by specific treatment (Kodani, 1942), but each has a com- 

 plicated fibrillar structure comparable to the fibrillar structure of a 

 muscle cell (which certainly could not be described as polytene myo- 

 sin). I should prefer to apply a term like "supermicellar chromosome," 

 and add that recent work by Freire-Maia et al. ( 1953 ) and Breuer and 

 Pavan (in press) agrees well with my point of view. In the develop- 

 ment of salivary cells they found cycles of higher and lower polyteny, 

 which, of course, excludes genuine polyteny. However, it is probable 

 that in one respect the polyploid and the polytene types are alike: both 

 produce a large template surface for protein synthesis. In Chironomus 

 the production of droplets at definite points of the salivary chromo- 

 somes is visible in vivo. 



I think that both types of structure show the nongenic parts of the 

 chromosomes at work and do not permit conclusions concerning in- 

 tranuclear differentiation as discussed above, though we may call it 

 thus in a limited sense. This, at least, is the way I must look at the 

 facts when taking into account the whole body of information. 



But one more remarkable fact should be mentioned which comes 

 as near to chromosomal diflFerentiation in development as can be 

 imagined. Beermann (1952) showed that the giant chromosomes of 

 dipteran cells have essentially the same structure in all different 

 tissues, for example, salivary, Malpighian, and intestinal cells (as 

 opposed to Sengiin, 1948; and Sengiin and Kosswig, 1947). But indi- 

 vidual regions may differ structurally. What is in one cell type a 

 group of clear bands may be in another a "bulb" with diffuse structure. 

 Could it be that these are regions which produce the non-genic 

 specific secretion product, the bulb being a group of bands in the 

 secretive phase? This would be a very important fact, though still in 

 agreement with our former conclusions on non-genic function of these 

 chromosomes. In a sense we might speak here of chromosomal diversi- 

 fication within different cells. But it is very different from erbungleiche 

 Teilung, if our interpretation of the background facts is correct. 



It might be surmised in this connection that the genie function of 

 the chromosomes in development is bound somehow to mitotic divi- 



