MUSEUM OF COMPARATIVE ZOOLOGY. 65 
layers of the body wall (i., ex.). Owing to the reagent, the body wall is 
shrunken from its contact with the operculum (op.). 
If one inquires what has been the histological conditions of this region 
antecedent to this stage, one must look to younger adjacent and mar- 
ginal zowcia, since they reproduce these conditions. I will again call 
attention to Figure 88, which represents a cross section of the body wall 
through the region of attachment of the kamptoderm of a young pol- 
ypide of about the stage of Figure 83. This, then, represents the neck 
of the polypide, and it is from about this region that the operculum and 
finally the regenerating polypides will arise. The cells are columnar, 
and stain deeply about the nuclei, and both cell layers are well devel- 
oped. Elsewhere in this same individual the body wall is composed of 
smaller, flatter cells, and two layers are not easily distinguished. The 
region of the future operculum possesses at an early stage some of the 
largest, most columnar cells of the body wall. The cells of this region 
do not, however, retain their peculiarly large size throughout life, but 
in the adult we find the same region occupied by a flat epithelium, 
nearly as thin as the epithelium shown in Figure 90. Meanwhile 
the epithelium of the rest of the body wall has become still more 
attenuated. The difference between the body wail of the operculum 
and that of adjacent regions is best shown by the greater abun- 
dance of nuclei under the opercular region when the stained stock is 
looked at in toto from the roof (Plate VIII. Fig. 71). The regions of 
the future opercula are seen, in young zocecia (Fig. 71, 4, 6), to be 
patches of densely packed nuclei. The opercula of older zowcia show a 
slight preponderance of nuclei, and thus indicate more numerous cells. 
It is from such a region, then, that the young regenerating polypide 
arises, 
As in the case of the marginal polypides, so here, the lips of the 
invagination pocket close and become fused to form the neck of the 
polypide (Plate X. Fig. 84). The later stages of the development of 
the regenerating polypides seem to be the same as those of the marginal 
buds, Figures 74 and 89 are, indeed, regenerating polypides. I cannot 
find any evidence that the alimentary tract, or any part of it, is formed 
in regenerating buds by a method differing in any essential particular 
from that in marginal buds, 
It is well known, however, that the degenerated polypide which forms 
’ in the old zoocium eventually disappears. Haddon 
a “brown body’ 
(83, p. 519) maintains that in the developing regenerated polypide 
“the walls of the stomach, or, more strictly, that portion of the stomach 
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