DISCUSSION 



nucleus, or at any rate in a particular stage of the spermatid, are in a very unique 

 morphological condition, as was determined by electro-micrograph, from which it 

 appears that the chromosomes at a particular stage are almost like membranes. 

 There is a very complicated kind of honey-comb appearance as if many membranes 

 were present, but had fused together in places. This kind of appearance is, I think, 

 almost unique to the spermatid, and it may, of course, have some relationship to the 

 proteins of the chromosomes, but it may also be in part responsible for the high 

 radio-sensitivity. This work was done on grasshopper spermatid, and I think it 

 might be very desirable that it should be repeated on Drosophila spermatid to see if 

 the structure was the same there. 



Dr. Loutit: Can Dr. Oster tell us anything of the metabolic activity of the spermatid 

 versus the spermatozoa or the spermatogonia. I understand that with regard to 

 bacteria there is a suggestion that, as it were, the resting stage is less mutable than the 

 stage which is actively metabolized. Would the stages in spermatozoa development 

 be variable in their metabolic activities ? 



Dr. Oster: I think that there is not very much direct evidence concerning the meta- 

 bolic activity of the different stages of spermatogenesis. However, from our general 

 knowledge of the process of gametogenesis and from genetical experiments we can 

 infer that the spermatid has a more active metabolism than the spermatozoon. This 

 conclusion is based on the following: 1. While the major portion of the genetical 

 material is not functioning in the spermatozoon and probably not in the spermatid, as 

 I mentioned earlier, the chromosomes of the spermatid are in the process of undergoing 

 chemical changes in their protein composition. 2. The major portion of the metabolic 

 activity of a spermatozoon is concerned with providing energy for movement while 

 the metabolic activity of the spermatid is concerned with a whole host of processes — 

 since during this period of transformation from the spherical spermatid to the conical 

 spermatozoon very drastic changes occur in its nuclear and cytoplasmic constitution. 

 It is certain that the differences in morphology which exist amongst the various stages 

 of male gamete development are associated with metabolic activities which differ 

 both quantitatively and qualitatively. 



In this connection it is worth mentioning some facts derived from studies on the 

 Cecropis silkworm, Platysamia cecropia. Experiments by Schneiderman, Ketchel, and 

 Williams invoking the effects of temperature, metabolic inhibitors, oxygen tension, 

 and carbon monoxide on the in vitro spermatogenesis of male germ cells of the silkworm 

 have indicated that the differentiation of the gametes is an aerobic process. They also 

 found that cytochrome oxidase, which is already saturated at an ambient oxygen 

 tension of only 5 per cent is the terminal oxidase involved in the maturation of the sex 

 cells. However, because this enzyme is so readily saturated by substrate and because it 

 is present only in relatively minute quantities in spermatids (as compared to sperma- 

 tozoa where it is ver>' abundant), there is a good possibility that this small amount of 

 terminal oxidase is insufficient to cope with the amount of oxygen which is constantly 

 diffusing to the spermatids via the highly permeable tracheal system. This, naturally, 

 would lead to the existence of a higher partial pressure of oxygen in spermatids than 

 in spermatozoa. Since the spermatids oi Drosophila are undergoing similar biochemical 

 and structural changes during their differentiation into spermatozoa it seems very 

 likely that a situation identical to the one in the silkworm is present in the fruit fly. 

 Evidence that the cytochrome system is also functioning in the pupae of Drosophila 

 was obtained by Wolsky in experiments with carbon monoxide which is a fairly specific 

 inhibitor of cytochrome oxidase in the dark. Thus these experiments, also, suggest the 

 existence of metabolic differences amongst the different stages and, as I mentioned in 

 my paper, these may bear some relationships to the differential radio-sensiji<ita y^Jy^rh" 

 we have described. X ■y 



267 '"^ 



