420 BICKFORD. Vou Ie 
body cavity, and is readily seen circulating rapidly in the 
regenerating ends. Allman describes this as a transparent 
liquid, in which are the following solid bodies :— disintegrated 
elements of food, cells which have doubtless been detached 
from the walls, and minute irregular corpuscles, which are 
possibly effete elements. It is in the hydranth that the food 
is dissolved ; of the nature of this solvent we know but little. 
According to G. Greenwood’s paper on “ Digestion in Hydra,” 
it doubtless originates as a secretion from the walls. The 
products of this digestion become the somatic fluid, which is 
mingled with water from outside, and propelled by the ciliated 
endodermal cells through the cavity of the. coenosarc, in 
currents which are rarely definite. In developing buds these 
currents possess great activity ; in limited cavities they usually 
pass in circular streams as in the hydranths, being here most 
likely connected with the preparation of aliment. Whether 
this fluid conveys the fully formed pigment to the regenerating 
ends, taking it from other cells, or whether it is formed zz 
situ, as a result of rapid growth and metabolism, is a point 
which remains to be determined by more minute histological 
study. 
This point is of interest in considering the question as to 
the source of the material used during the extremely rapid 
growth and regeneration of the hydroids studied. In many 
instances fully formed hydranths were obtained zz about 
eighteen hours after the old ones were cut off. The compara- 
tively large size of some of the hydranths regenerated on very 
short fragments indicated that the supply of reserve material, 
in some form, must be abundant. The amount of pigment in 
the regenerating ends would lead one to suspect that there 
may be a connection between it and this reserve supply ;— 
this also is a point worthy of histological investigation. 
(2) The experiments were made with these hydroids in the 
following manner :— Fresh stems of hydroids were taken from 
colonies, the hydranths cut off, and the stems cut in pieces 
of varying sizes. These were placed in a bowl of fresh sea 
water and covered with glass to exclude the dust. Some 
extremely short pieces were examined under a high power 
