EMBRYOLOGY OF STOMOTOCA APICATA 
345 
nine or ten tentacles according to the stage of development. Ten 
seems to be the number of tentacles in the fully developed hydroid, 
polyp. The oldest polyps that I reared, five days old, had this 
number; and Professor Brooks describes the hydroid, which he 
found on the lower surface of the shell of the living Limulus, and 
which had medusa buds developed, as having only ten tentacles. 
The hydranths that I reared in the Laboratory corresponded with 
those found by Professor Brooks and I have no doubt that they 
were the same species. The primary and secondary tentacles 
arise from the same level so that they may be said to constitute 
one whorl. The five primary tentacles, however, are longer and 
project forward ; while the secondary ones are shorter and extend 
backward. The tentacles are well armed with thread cells which 
are arranged around the tentacles in clusters at short distances 
from each other, from one end of the tentacle to the other. These 
groups of thread cells become closer together as the distal end 
of the tentacle is approached. 
A thin, delicate perisarc is secreted early in the development 
of the hydranth. It adheres closely to the root and stem. It 
does not extend the entire length of the stem; but stops a little 
distance below the circle of tentacles. In fig. 31a polyp is shown 
in which the coenosarc has retracted for some distance in one of 
the hydrorhiza and left the delicate tube of perisarc empty. 
StnVIMARY 
1. The eggs are laid at a regular time, about five o'clock in 
the morning. They are set free by the breaking down of the 
epithelial layer of the ovaries. 
2. The egg is spherical and measures .14 mm. in diameter. It 
is destitute of a membrane when laid, and none is subsequently 
developed. The cytoplasm is dense and opaque. 
3. Maturation takes place after the eggs are laid ; and fertiliza- 
tion takes place very soon. Details of fertilization could not be 
made out because of opacity of the egg. 
4. Cleavage is total, equal and nearly regular, especially in 
the early stages. Protoplasmic threads or bridges connecting 
