176 SABELLA. 
The caudal appendage is long in some specimens, commonly extend- 
ing a line anda half. It consists of eight or ten enlargements, suscep- 
tible of some alteration of form. 
Numerous ova are produced at different times of the year, m June, 
August, and in October. They are generally purple, consisting of a 
darker nucleus, within a gelatinous sphere. A specimen having been in- 
jured in the third week of October, by separating a congeries of tubes, a 
vast quantity of purple ova issued from about the root of the cleft. The 
parent itself was coloured by the presence of the ovarium, for by this 
organ are these creatures greatly affected during the season of propaga- 
tion. They become brownish or dingy white, from a fine ruddy colour, 
when the spawning season is over. 
On removal to a watch-glass, the same specimen continued dis- 
charging thousands of ova, all of a beautiful purple colour, and regular 
ovoidal form. But neither they nor others have afforded any progeny. 
This is a timid, lively, active creature, whose most, prominent pro- 
perty is constructing itself an artificial dwelling of the grains of commi- 
nuted sand, intermingled with shelly fragments, or other indurated sub- 
stances. But there seems a great difference in the solidity of the dwelling 
according to the position of the tube, or perhaps the variety of the archi- 
tects, which has never been the subject of sufficient observation. Thus 
we find the fabric, when a cylindrical segment, running over some flat- 
tened surface, firm, durable, and capable of great resistance. It is not 
easily crushed. On the other hand, when cylindrical or alveolar, it ap- 
pears to be always more brittle. Most of the dwellings of the Sabella 
are lined with a fine silky substance, formed of an exudation escaping 
from the body, which, consisting of indurated gelatinous matter, is very 
conspicuous on breaking up the alveolar mass of some old congeries. 
The animals testify a decided preference on choosing the materials 
of their habitations. While always preferring sand and comminuted shell, 
pounded glass is sparingly and reluctantly employed, and unless for a 
few fragments, it is soon entirely rejected. 
But there is a striking difference in the character of the tahee One 
is short and confined, extending little beyond mere accommodation for 
