412 THE BIOLOGY OF HYDRA : 1961 



DISCUSSION 



EAKIN: When the use of oxaloacetate as a source of COo was 

 mentioned, during the previous discussion, the question came to 

 my mind as to whether or not increased CO^ tension would 

 reverse the inhibition of regeneration caused by hpoic acid. I 

 would be very chagrined if we found out that the effect of oxaloace- 

 tate was merely to build up the CO2 level. 



BURNETT: Were yoiu- normal hydra budding when you cut them 

 through the middle? 



EAKIN: Yes, we always use hydra that had one (or preferably 

 two) buds in order to insure that our organisms were in an optimal 

 state of nutrition. The use of the words "mid-stomach cut" was 

 to indicate a severance in the region mid-way between the hypos- 

 tome and the point of budding. 



Perhaps I should explain how the differential counts on the 

 developing interstitial cells were made. These counts were made 

 on longitudinal sections through the center of the coelom. The 

 ratio of interstitial cells (at the four stages of maturity) to total 

 cells is a maximum at the hypostome and decreases as one pro- 

 gresses proximally until a minimum occurs just before reaching 

 the budding area. Past this point the ratio increases markedly, 

 the final stages of maturation into cnidoblasts being especially prom- 

 inent. The counts were made in the area between the site of sever- 

 ance and the line demarcating the minimum concentration of 

 interstitial cells, thus excluding the budding area. 



