NORTHIA. 



137 



The worm lives in a tube which has a singularly exact resemblance 

 to the barrel of a quill. It is about 4 inches long, and the upper 

 portion is thinner than the lower, which is tough, and not easily cut 

 with a knife. 1 made a vain attempt to form it into a pen. 



No. XX. — Northia tubicola. 



W 





1 a. Cephalic segment with three long subulate tentacula. 



1 8i 2 a, b. Tentacular cirri. 



2 c. The mouth, upper lip, formed of two large egg-shaped tubercles. 



3. Section of anterior part of body, showing the cirrus above and below 



the foot. 



4. A spine, one on each fascicle of the foot. 



5. Forceps, two on each fascicle of the foot. 



6. Lanceolate bristles, many on each foot, curved at the tip, and very sharp 



and double-edged at the point of curvature. 



Let us see if, in its curious structure, we can find a key to the 

 habits of the animal. We learn from Miiller that it lives in soft 

 mud, and one unceasing object of its life is the capture of prey. For 

 this end, it must protrude the anterior portion of the body beyond 

 its tube, and raise itself above the surface of the mud, — and remain, 

 in this position, on watch. To enable the worm to do this with 

 ease, is, I conjecture, the office of the forceps-like bristles of the 

 feet : with their ends, it may hook itself to the rim of the tube, and 

 thus obtain a support without the waste of muscular power, A long 

 watch is thus rendered less irksome, while at the same time the 

 capacity to seize upon a passing prey is increased. 



The prey caught, analogy leads us to conclude that the worm will 

 instantly retreat and sink within its tube, where it can feed without 

 disturbance or fear. But as the entry and passage are narrow and 

 unyielding, it seems to follow that the prey should be held by the 

 mouth alone when in the act of being dragged within the tube, and 



