60 SQUIRTS, POLYPS, AND JELLY-FISHES. 
nity at large. Each little active polyp is situated in 
its own chitinous cup, the different cups being ar- 
ranged ina double series along the connecting axis. 
Between these cups, at certain seasons of the year, 
may be observed a number of larger and somewhat 
urn-shaped bodies, the gonothece, from buds con- 
tained in which the eggs necessary for the perpetu- 
ation of the species are developed. These liberate 
minute ciliated bodies, known as ‘ planule,’ which, 
after enjoying a short independent existence of their 
own, attach themselves, and grow up into the grand- 
parental form. 
The commoner of the two forms of sea-fir found 
on our coast is the silver sea-fir (Sertularia argentea, 
Pl. 4, Fig. 7), so named from the general white- 
ness of the fronds, and found from low-water 
mark to a depth of 100 fathoms or more. It is 
the common ‘sea-moss’ that is so extensively dis- 
played in the shops along the sea-shore, and used 
by florists for decorative purposes. A smaller spe- 
cies, the dwarf sea-fir (Sertularia pumila, Fig. 10), 
attaches itself to the ordinary brown rockweed or 
fucus, also to pebbles, and to various dead ana 
living shells. 
Growing in bunches much like the sea-firs, but ap- 
pearing thinned out by reason of the distance of the 
polyps from one another, is the form known as Pen- 
naria (Pl. 4, Figs. 3, 12), whose fronds can be easily 
distinguished by the black color of the branches. 
The polyps which terminate the branches are ex- 
ceedingly minute, of a bright red color, and fur- 
nished with three circles of tentacles. In probably 
