ALLISON L. BURNETT 427 



cell proliferation in the hypostomal region and constant cell death 

 at the extremities, hydra is able to grow continually yet maintain 

 its form. 



Numerous grafting experiments conducted by several different 

 investigators, notably Rand (15, 16, 17) Hefferman (8), Browne 

 (2), Kolitz (11), Burt (4), Issajew (10), Rand, Bovard, and 

 Minnich (18), Tripp (19), Mutz (14), Yao (23, 24, 25), demon- 

 strated that the hypostomal region of hydra is the "dominant" 

 center of the animal and will induce polyp formation at the site 

 where it is grafted to the body column of another hydra. Similarly, 

 it was shown by many of these workers that tissues of the develop- 

 ing bud will induce hydranth formation in another hydra at the 

 graft site. 



From the obser\ations cited thus far in this paper, it would 

 appear that the hypostomal region of the animal is one which is 

 engaged in constant growth activities. In this highly metabolically 

 active region a growth inhibitive principle is produced which 

 passes down the stalk and inhibits cellular dixisions in the adja- 

 cent gastric region. In the budding region of the hydra, the in- 

 hibitive principle presumably does not exert its affect and the cells 

 in this area take on properties similar to those in the hypostomal 

 growth region. In a sense, it may be stated that a new growth 

 region is created in the budding region, for both the hypostomal 

 and budding regions engage in cell divisions which lead to the 

 formation of a new polyp. If this is correct, then it must be assumed 

 that cells in the gastric region possess the potential of growth 

 and rapid cell division, but that these cells are inhibited in some 

 manner from performing these vital functions while they are lo- 

 cated in the gastric region. 



This paper will attempt to answer the following basic questions. 

 What accounts for the high metabolic activity of a particular area? 

 Does hydra possess a specific growth inhibitive principle which 

 is produced in the hypostome? Does this principle become inac- 

 tivated as it diffuses down the body column towards the budding 

 region? Does this principle inhibit cellular divisions in the area 

 in whch it is produced? Are there specific substances responsible 

 for the growth and inductive potential of the hypostome? 



None of the experiments designed to answer these basic ques- 



