60 SQUIRTS, POL r PS, AND JELLY-FISHES. 



nity at large. Each little active polyp is situated in 

 its own chitinous cup, the different cups being ar- 

 ranged in a 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 gonothecse, 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 ' planulse,' 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, 

 PI. 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 (PI. 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 



