114 ERNEST WABREN. 



group of endoderm cells. The nuclei of the cells lose 

 their chromatin, tend to become homogeneous and ultimately 

 disappear. 



There may be a marked hypertrophy of the cells, as is 

 shown in figs, r, G, where one or more ectoderm cells have 

 formed an eruption three or four times the height of the 

 ectoderm layer. 



In cross-section of the ccsnosarc there are seen in the endo- 

 derm lai'ge, oval, honeycombed areas with blackened walls, 

 taking the place of a number of cells, and with their long axis 

 pointing towards the centre (fig. b). In fig, e an example is 

 illustrated where vacuolatioii is late in appearing. In figs, h 

 and I pigment granules are being formed in immediate con- 

 tact with an endoderm nucleus, and in fig. i the nucleus has 

 become homogeneous in character. In figs, n-p the course of 

 change in an endoderm gland-cell is shown. The normal 

 rounded masses of secretion are shown iu fig. n ; in fig. o the 

 beginning of pigment formation and v;icuolation is seen in the 

 middle of the cell, and in fig. p the condition is much more 

 advanced. The ordinary cytoplasm of the cell is not com- 

 pletely involved even in fig. p, but the nucleus has become 

 homogeneous and apparently moribund. 



In surface view of tlie hydroid the areas involved in this 

 degeneration in the endoderm are rounded, oval, or often 

 spindle-shaped in outline (text-fig. 5, a, b) and of moderately 

 uniform size (long axis about 15^). Soinetimes elongated, 

 rather thick bands are formed (text-fig. 4, a and 5, c). In 

 the ectoderm the areas are usually narrow, elongated, or 

 fusiform (text-fig. 5, d-h). 



The long axes of the elongated blackened areas in the 

 endoderm are in the long axis of the coenosarc. The narrow 

 streaks in the ectoderm are also frequently in the long axis, 

 but sometimes they may lie more or less transversely (text- 

 Fig. 4.— Thniaria tubulif ormis (M.-Turn.). Fio-. a, X 425. 



Fig. B, X 1200. Fig. c, X 900. Fig. n. x 10,000. Fig. e, x 1200. 



Fig. F. X 1400. Fig. G, X 700. Fig. h, x 2000. Fig. i, x 1200. 



Figs. J-M, X 1500. Figs, n-p, X 1600. 



