862- THE AMERICAN NATURALIST.  [Vow. XXXIII. 
several hours. By this process the cells could be distinguished 
easily in any part of the hydroid where the perisarc was not too 
dense. 
If the parts of the colony are taken up in detail, they will 
be found to agree on the whole with the account of Penna- 
ridæ given by L. Agassiz (1). The main stem arises from the 
hydrorhiza by a slightly geniculate course, giving off branches 
alternately at each bend. These branches may again divide. 
Each branch gradually tapers from the base, bearing on the end 
a single hydranth of large size. About the origin of a branch 
there are several annulations, from eight to twelve, and several 
on the branch itself near its origin. Around the base of the 
hydranth, which is more or less bottle-shaped,—the neck of 
the bottle corresponding to the distal end of the hydranth, — 
there is a row of tentacles, twelve in number. These tentacles 
round off at the end much the same as in all Tubularidæ. 
They are termed the “long tentacles ” to distinguish them from 
the “short tentacles,” which are more or less irregularly arranged 
around the oral end of the hydranth. These latter are much 
shorter than the long tentacles, and are arranged in two whorls. 
They are terminated by a knob, or globular tip, which is sup- 
plied with numerous nematocysts. There is a great deal of 
variation in the number of the short tentacles, due chiefly to 
the age of the hydranth; the older hydranth having the most. 
The Medusz arise from the hydranth anywhere between the 
rows of tentacles. They are in direct communication with the 
body cavity until nearly mature, when the connection becomes 
closed and the Medusz are set free. 
HisToLoGy oF PARTS. 
Hydrorhiza.— There will be found in the hydrorhiza a very 
dense, hard perisarc on the upper surface. It is more than 
twice as thick here as on the opposite side and much denser. 
The ectoderm upon this surface of the hydrorhiza presents an 
almost structureless appearance. It is chiefly made up of very 
fine granules of protoplasm. There are scattered around in this 
space occupied by the ectoderm several rather large oval or 
