194 TEREBELLA. 
many of which lead to fallacies. I do not deny, by any means, that 
there may be some fixed members, and some fixed forms. But in ex- 
amples innumerable, so many, that in fact I fear to refer to them, many 
such details are absolutely equivocal. Some things, such as dimensions 
and proportions, which we reasonably deem very essential, are unfortu- 
nately no less so. I am far from disparaging the labours of such learned 
naturalists as have followed the preceding course, but I cannot suppress 
my opinion, that if persons so skilful devoted their care to perfect living 
specimens, instead of to those chiefly dead or disfigured, they would have 
found far more prominent, more permanent and satisfactory features, 
whereon to found their systematic arrangements. 
Undoubtedly the number of the tentacula in the Terebella figulus is 
dependent on age, or it may denote differences not yet sufficiently re- 
cognised. None, except the fine specimen represented, have had above 
twenty-five. But in this individual that number was doubled. Those 
of this specimen seem to be all different dimensions ; observing, however, 
that the aspect of such variable organs is wonderfully modified. They are 
stouter than those of the preceding species, and when extended com- 
pletely they reach nine inches, that is above twice the length of the body 
of the animal, being thus capable of sweeping a spacious area. Their 
natural colour is uniformly brown, or tending to carmine, often shewing 
dark tips. When stretching far, they resemble a strong whitish horse 
hair. 
In fabricating its dwelling, this creature gives an evident preference 
to mud, as the most suitable of materials. Should a quantity of this 
substance, of sand, and of comminuted shells be alike accessible, the first 
is always preferred, and the last always rejected, or reluctantly used. 
The Terebella is continually in quest of materials. The contents of a 
watch-glass introduced within its reach at night, have generally disap- 
peared against morning. 
If the animal be dislodged from its tube, the body becomes closely 
coiled up, but the tentacula speedily search around, sweeping up every 
thing within their reach ; and if the materials are abundant, a covering is 
speedily formed. It contracts greatly while the earlier part of the edifice 
