864 THE AMERICAN NATURALIST. [VoL. XXXIII. 
cells of the endoderm, and project out into the cavity about half 
of their length. The nuclei are of different sizes, according to 
their position in the endoderm. Some of the nuclei found in 
the digestive cells are twice as large as those occurring in the 
other cells. Between these four groups of specialized digestive 
cells the endoderm is quite regular. 
Mesoglea.— The mesoglea presented the same appearance 
and was of the same thickness in each region. 
ORIGIN AND DEVELOPMENT OF THE MEDUSA. 
The Medusa takes its origin from the hydranth, between the 
rows of tentacles. There is no definite region on the hydranth 
from which the buds arise. However, they are more abundant 
near the base of the second or “longer tentacles.” The num- 
ber of buds which may be found upon the hydranth at one time 
varies. In case the hydranth is giving origin to male Medusz 
there may be four or five, but usually two or three are all that 
will be found. The hydranths which give rise to female 
Medusz generally give off only one. One exception was noted 
to this, but it holds true in the majority of cases. When a 
hydranth gives origin to more than one Medusa, they will not 
be in the same stage of development. I have found the two 
extremes on the same hydranth — the buds just forming and 
the mature Medusz ready to be set free, together with several 
intermediate stages. 
The Medusa bud arises as a simple evagination of the 
hydranth. The bud is hollow and supplied directly with nour- 
ishment from the circulating currents of the hydranth. As a 
bud becomes larger and longer, many interesting changes take 
place. In the mature Medusa the parts correspond to the type 
Hydromedusa, yet the manner in which the several layers origi- 
nate is very different. Agassiz states that Pennaria develops 
its Medusz in the same way as Coryne and Bougainvillia do (2). 
While the several parts are the same in Coryne and Pennaria, 
yet their origin and “development are very different. The first 
sign of the formation of the Medusa bud is shown by a thick- 
ening of the cells of the ectoderm. This change produces a 
