344 
SAMUEL RITTENHOUSE 
down on the broad anterior end, from which the hydrorhiza are 
given off, while the opposite end forms the hydranth and develops 
the mouth and tentacles. The planula of Stomotoca instead of 
settling down on the anterior end, becomes attached by the whole 
length of the larva. That is. the planula does not become trans- 
formed into a hydranth but forms the root ; and the first hydranth 
is given off from the root as a bud. The planula changes its shape 
about the time it is ready for attachment. The enlarged anterior 
end is reduced in size and the larva becomes spindle shaped . Then 
usually about the time the bud which will form the hydranth 
appears, the primary root branches, giving off one oi two secondary 
roots; so that when the hydranth is developed it may have two, 
three or four hydrorhiza as shown in figs. 27 to 32. The settling 
down and attachment of the planula of Stomotoca apicata is 
very much like that which takes place in Turritopsis nutricula, 
the development of which was described in a recent paper. 
Professor W. K. Brooks in his work on ^'The Life-History of 
Eutima^' (1884) has shown that the planulae of Eutima, Tur- 
ritopsis and Hydractinia form roots and that the hydranths 
arise as buds from the roots. 
DEVELOPMENT OF THE HYDRANTH 
After the larva has become attached it very soon develops 
a bud which is the beginning of the hydranth. A circle of small 
projections make their appearance very early around the distal 
end of the hydranth bud ; these are the rudiments of the tentacles 
and are usually five in number. Occasionally a hydranth bud 
has six tentacular projections and thus gives rise to six primary 
tentacles. The mouth is now developed, as a slit breaking through 
the two germ layers at the apex of the young hydranth in the center 
of the whirl of tentacular buds. About a day later more tentacles 
appear. These secondary tentacles alternate with the primary one. 
The secondary tentacular buds do not all appear simultaneously ; 
but are usually added one or two at a time until the second cycle 
of tentacles is completed and the hydranth has ten tentacles in 
.all. Thus we may have young hydranths with six, seven, eight. 
