24- NATURAL ARRANGEMENT OF INSECTS. 



however, their branchiae placed only on the middle of 

 the body. Their structure is more simple than that of 

 the Errantes, — to which, through the medium of the 

 AricidoB, consisting of the genera Cirratulus, Ophelia, 

 Aricia, Sec, they form the passage. They inhabit the 

 sands of the ocean, at the depth of one or two feet ; and 

 they betray their retreat by the small convoluted threads 

 of sand formed on the surface. Fishermen make great 

 use of them to bait their hooks ; and, when caught, they 

 stain the fingers with a yellow liquid. 



(22.) The third and last family, the Errantes, is the 

 largest of all ; they form several tribes, and consist of 

 a multitude of genera. They are the most highly or- 

 ganised of the whole of this group ; having a very dis- 

 tinct head, furnished with antennae, eyes, and almost 

 always a protractile proboscis armed with maxillae : 

 each ring of their body bears a pair of feet, the structure 

 of which varies considerably, — sometimes placed on the 

 back and the belly, — and each consistingof two tubercles ; 

 yet both are occasionally united, and their extremity is 

 furnished with a pencil of setae. When the feet are 

 united, and form but one organ, they are generally fur- 

 nished with a pair of cirrhi, or fleshy filiform append- 

 ages, at the base of which the branchiae are seated. 

 The setae themselves, Avhich decorate the feet, are usu- 

 ally rigid and retractile, and they then serve for loco- 

 motion and the defence of the animal ; but they are 

 also often very long and flexible, and cannot then be 

 withdrawn into the body, but cover it like a dense fur. 

 They walk and swim well ; but usually dwell beneath 

 stones, among shells, or buried in the sand. A mucus 

 that exudes from them, frequently forms around them 

 a sort of tubular case, which they inhabit, but which is 

 of a less compact and solid structure than that observed 

 in the Tnhicoles; and besides, the animal has the power 

 of quitting it to seek its food and prey. They are all 

 marine animals. We will briefly enumerate the tribes 

 they constitute, and the more conspicuous genera. 



(23.) Those without cirrhi at the base of their feet 



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