306 THE BIOLOGY OF HYDRA : 1961 



Here again we must raise the question: What is it that is being 

 moved from the old jDart to make the new? Are cells moving? Are 

 old cells breaking down to give substances that are moved and 

 reutilized? We do not yet know the answers. 



At Indiana, Mr. Hartman (9) undertook to find differences 

 among the tissues taken from different parts of a colony in re- 

 spect to their capacities when dissociated. No differences were 

 found among tissues from stem, stolon, or early hydranth buds of 

 Campamdaria. Tissue taken from adult hydranths, however, did not 

 reconstitute. This led, naturally, to tests of different stages of hy- 

 dranth development. When a late stage of hydranth development 

 was used, but one in which there was not yet any visible differentia- 

 tion, Hartman found that the tissues reaggregated and within a 

 few hours produced differentiated hydranth parts with an ir- 

 regular organization. Two examples showing patches of tentacles, 

 and in one case a hypostome, are illustrated in Figure 8. Evidently 



Fig. 8. Two examples of the irregular structures which differentiated 

 when tissues from a late hydranth bud were dissociated and allowed to re- 

 aggregate. There are patches of well developed tentacles, and in the 

 example at the right there is a hypostome (From Hartman, ref. 9). 



each region of the scrambled tissues was already set in the course 

 of its differentiation. A further test of the distal tissues of buds at 

 this age showed that they were like the whole in making irregular 

 structures at once. But the tissues taken from the proximal halves 

 of such buds reconstituted according to the same pattern as stem, 

 stolon, or early bud tissue. 



