CEL];Ur;AR DEGENl!]BA'l'[ON AND FOEMATION OF I'Kl.MKNT. 105 



whole may become so reduced that even in those parts where 

 a certain amount of new growth is occurring- the physio- 

 logical functions are not completely normal in character. 

 Notwithstanding this, however, the older portions of the 

 colony show much greater pigmentation than the younger 

 portions. 



I can find no clear evidence that the pigmented condition 

 is associated with the presence of any parasitic organism. 

 Bacteria and parasitic protozoa were carefully searched for 

 in all the preparations, hut no certain trace of their occurrence 

 could be detected. The rodlets of pigment seen in unstained 

 preparations of Sertularia operculata certainly mimic 

 stained bacteria in an extraordinary manner ; but their mode 

 of origin negatives the view that they are of bacterial nature. 

 To distinguish and separate the agencies involved in this 

 pigment-degeneration, experiments with living hydroids 

 would be of great interest ; but the facilities of a marine 

 laboratory would be essential before the investigation could 

 be undertaken. 



The study of cellular degeneration in a simple organism 

 with a relatively simple histological structure is of some 

 interest, as it is likely to lead to a better understanding 

 of the phenomenon hs it occurs in higher animals and in man 

 himself. 



We know that in the case of white man exposure to the 

 sun usually induces freckles and a general darkening of 

 the skin. This condition is due to the presence of melanin 

 granules in, and between, the epithelial cells. At the present 

 time it is more generally held that the melanin is actually 

 produced l>y the epithelial cells, and is not, as was formerly 

 thought, brought to them by wandering mesoderm cells which 

 had elaborated it from the hajmoglobin of the blood. The 

 melanin gninules are often found between the epithelial cells, 

 and if the granules had become scattered by the disintegra- 

 tion of some of the pigment-producing cells, we should arrive 

 at a condition which is closely paralleled by that which is 

 sometimes seen in hydroids. It is not to be supposed, however. 



