278 THE AQUARIAN NATURALIST. 



dwelling, according to the position of the tube, or 

 perhaps depending upon the resources of the architect. 

 Thus we find the fabric, when presenting the shape of 

 the segment of a cylinder, attached to some flattened 

 surface, firm, durable, and capable of great resistance. 

 It is not easily crushed. On the other hand, when 

 cylindrical or alveolar it appears to be always more 

 brittle. Most of these dwellings of the Sabella are 

 lined with a fine silky substance formed of a gela- 

 tinous material that exudes from the surface of the 

 body. 



These animals testify a decided predilection while 

 choosing the materials for their habitations, always 

 preferring sand and comminuted shell. Pounded 

 glass is sparingly and reluctantly employed, and, 

 unless for a few fragments, is soon entirely rejected. 

 But there is a striking difference in the character of 

 the tubes : one is short and confined, giving little 

 beyond mere accommodation for the body ; while an- 

 other is considerably prolonged, so as to afford a safe 

 retreat in times of danger. The architect of a third 

 seems to persist in advancing the fabric as long as it can 

 procure materials, and never seems weary of working. 



Night is the chief season of this architectural 

 labour, though the worm is seldom guilty of perfect 

 idleness. 



By means of the tentacular organs and the cleft in 

 the anterior part of the head, grains of sand are 

 selected and adapted where they are required, a glu- 

 tenous secretion securing each particle in its proper 

 place ; and thus the growing structure is progressively 

 extended. 



