166 DONALD WALTON DAVIS 
dishes after feeding or disgorged by the animals tended to foul 
the water. It was found, furthermore, that the animals thrived 
quite as well without this attention, doubtless being supplied 
with sufficient food in the form of minute organisms. Under 
these conditions specimens decrease in size somewhat at first and 
after a time become lighter in color. In other respects they 
appear to remain in perfectly normal condition. 
In order to study the internal structures, specimens were fixed 
and sectioned. The larger mesenteries can be seen in sections 
cut by hand, but smaller mesenteries are sure to be overlooked 
if dependence is placed upon that method of examination. My 
specimens were therefore stained, embedded in paraffin, sec- 
tioned, and studied with the compound microscope. 
For narcotizing, A. G. Mayer's method of immersion in a 3/8 
mol. solution of magnesium chloride has proved entirely satis- 
factory. After a half-hour in this solution the specimens are 
thoroughly stupefied and almost invariably well extended. 
Animals in good active condition tend to expand in this solution, 
even though they may at first contract from the mechanical 
stimulation incident to immersion. Unless fine histological 
fixation is desired, 4 per cent formalin is a convenient and satis- 
factory killing agent. From this the specimens may be trans- 
ferred immediately to 70 per cent alcohol. Staining in toto for 
eighteen to twenty-five hours in Kleinenberg's haematoxylin 
brings out well the mesogloea, which gives the best evidence of 
the position of mesenteries and of the longitudinal muscles upon 
them. 
Some of the specimens whose regeneration is recorded divided 
under observation in the laboratory; others were discovered, 
either in their natural habitat or in the laboratory, at the close 
of division or immediately following separation of the parts. 
Nearly all of the other specimens examined have shown exter- 
nally some portions of regenerated material. 
