HABITS OF SABELLA ALVEOLARIA. 277 



One of the commonest of these little architects is 

 the Sabella alveolaria (PL V. fig. 6), the length of 

 which is seldom more than three-quarters of an inch. 

 Its head, or anterior part, is provided with numerous 

 filamentary tentacula (about eighty in number) . These 

 organs are extremely flexible : one surface has a 

 groove in the centre, and when completely extended, 

 may be observed to be toothed on both sides, so as in 

 some measure to resemble the weapon of a saw-fish 

 in miniature. The body is round, and composed of 

 numerous segments, some of which are provided with 

 bunches of minute lateral setae. A slender caudal 

 appendage, generally folded up on the body, termi- 

 nates its extremity ; it consists of eight or ten joints, 

 and is susceptible of some alteration of form. 



Numerous eggs are produced at different times of 

 the year, especially in June, August and October. 

 They are generally of a purple colour, consisting of a 

 darker nucleus within a gelatinous sphere. A speci- 

 men having been injured in the third week of October 

 by separating a congeries of tubes, a vast quantity of 

 purple ova issued from the wound ; and on being re- 

 moved to a watch-glass, the same specimen continued 

 discharging thousands of ova, all of the same beautiful 

 colour and regular ovoidal form. But neither they 

 nor others have afforded any progeny. 



The Sabella alveolaria is a lively active creature, 

 whose most prominent property is the power of con- 

 structing for itself an artificial dwelling, composed of 

 grains of comminuted sand intermingled with shelly 

 fragments, or other indurated substances. But there 

 seems to be a great difference in the solidity of the 



