374 THE BIOLOGY OF HYDRA : 1961 



Schlottke (25) made very careful cytological studies and, more- 

 over, suggested that David's histological sections were heavily para- 

 sitized. Schlottke's observations can be summarized as follows. There 

 appears to be an aging process in ectodermal cells which is char- 

 acterized by nuclear changes, e.g., pyknosis. He noted that the cells 

 move from the ectoderm into the endoderm after they degenerate 

 and observed the appearance of what he called "guanine deposits" 

 as the remains of cells which had been resorbed into the endoderm. 

 Schlottke also noted that degenerating nematocysts tended to move 

 into the endoderm. 



Schlottke's early view is quite similar to that of Brien (5) who, 

 in 1953, published evidence, based upon marking experiments, that 

 there is a continual formation of new cells in the region around 

 the hypostome and that this is followed by a continual, slow (but 

 systematic ) movement of cells down over the surface of the column 

 of the hydra body to the foot where death and resorption take 

 place. One of the reasons that coelenterates are valuable in aging 

 studies arises from the fact that certain representatives of the phy- 

 lum make it evident that there is no necessity for senescence in 

 metazoa per se, just as certain immortal clones of protozoa demon- 

 strate (26) that sexual reproduction is not necessary for clonal 

 immortality. 



A most charming description of a long-lived, and proba]:)ly 

 immortal coelenterate, was published by Ashworth and Annandale 

 in 1904 ( 1 ) : "We have, during the last two years, made a series 

 of observations upon specimens of Sagartia troglodytes (later re- 

 identified as Ceretis pediincitlatiis) which are at least 50 years old 

 and have thought it worthwhile to give a somewhat detailed account 

 of these. So far as we can ascertain, there is only one other recorded 

 case of longevity in coelenterates and very few in the whole of the 

 invertebrates. These specimens of Sagartia were collected by Miss 

 Ann Nelson (Mrs. George Brown) on the coast of Iran some few 

 years previous to 1862 (the exact date has not been recorded) and 

 were placed in bell jars containing sea water. In 1862, they were 

 transferred to the care of Miss Jessie Nelson, in whose possession 

 they still remain and to whom we are indebted for the opportunity 

 of observing these interesting anemones. Sixteen of the original 

 specimens are still living, so that they have lived in captivity for 



