152 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
tion of the upper zone is simply corrugated and folded longitudinally ; 
that of the lower exhibits thickened patches a millimeter or more in 
diameter and fairly closely set. Of these patches there are three or four 
rows running around the column. The secretion of all three regions has 
a fibrous appearance due to the fine, sinuous corrugations which run 
around the column, and are the expression of differences in the thickness 
of the secretion. The effect is as though the secretions had been formed 
as rings, more or less complete, which had been crowded downward by 
successive additions above. In the region which bears the hairs the 
same appearance is shown, under a low magnification, by the secretion 
which constitutes the hair. This is a hollow thin-walled cylinder, which 
gradually diminishes in size from its base, where its diameter is about 
0.2 mm., to its free end. The hairs attain a length of 25 mm. or more, 
and are so tough that they form for the actinian a means of secure 
anchorage in the mud. The corrugations of the wall of the hair which 
run around it are not due to folds of the secreted substance, for optical 
longitudinal sections of the hairs show that the inner surface of the tube 
is smooth. When the animal is thrown into alcohol this case, with its 
tuft of matted hairs, is readily detached from the column, but a careful 
examination of those case secretions which are not thus artificially sepa- 
rated shows that there are at intervals exceedingly minute filaments 
running out from the surface of the animal to the inner surface of the 
case, and I am convinced that these are the minute filaments described 
as arising at regular intervals from the surface of the bulbous portion 
of the column. I believe that a single filament is enclosed in each of 
the hollow hair-like appendages of the case, and that the form and size | 
of these hairs is, in part at least, determined by the presence and shape | 
of the filaments of the column. The lower part of the case is much 
wrinkled lengthwise, and projects to some distance (5 or 10 mm.) below 
the base of the column. It has the appearance of having once sur- 
rounded the enlarged end of the column and having been slipped back- 
ward, its elasticity causing it. to become wrinkled like the mouth of a 
meal-sack that is tied. The hair-like processes surround this open end 
of the case and project beyond it. 
