ANNULOSA: ANNELIDA: 2/1 



The head is distinct, and carries eyes and feelers, whilst the mouth is fur- 

 nished with a large proboscis, and often with two horny jaws. In the 

 Eunicea the branchiae are usually well developed and of large size, and the 

 mouth is armed with seven, eight, or nine horny jaws. Eunice gigantea 

 attains sometimes a length of over four feet, and may consist of more than 

 four hundred rings. 



All the Errant Annelides are marine, occurring in all seas 

 from the Arctic Ocean to the equator, and extending to great 

 depths. A few forms (e. g., Tomopteris] are pelagic. Others 

 live in sand and mud ; whilst others hide under stones, or in 

 fissures in rock-pools ; and others, again, bore holes in calca- 

 reous rocks. A few live as " commensals " on other animals. 



DISTRIBUTION OF ANNELIDA IN TIME. Of the Annelida 

 the only orders which are known to have left any traces of 

 their existence in past time are the Tubicola and the Errantia ; 

 of which the former are known by their investing tubes, whilst 

 the latter are recognised by the tracks which they left upon 

 ancient sea-bottoms, or by their burrows in sand or mud, or, 

 more satisfactorily, by their horny jaws, remains of this latter 

 nature being known from deposits as old as the Lower 

 Silurian. 



Tubicolar Annelides are known to occur from the Silurian 

 rocks upwards. The well-known Silurian fossil Tentaculites, 

 has been often referred to the Tubicola, but is almost certainly 

 Pteropodous. Cornulites* Serpulites, Ortonia, Trachyderma, 

 Spirorbis, and Conchicolites are, however, genuine Silurian 

 Tubicola. The Microconchus carbonarius is a little spiral Tubi- 

 colar Annelide, nearly allied to the Spirorbis (fig. 130, b) of our 

 seas, which is not uncommonly found in strata belonging to 

 the Carboniferous period ; and the genus Spirorbis itself is 

 represented even in the Silurian period.- 



CLASS III. CH^TOGNATHA (Huxley). Elongated cylindrical 

 animals having the hinder extremity of the body furnished with an 

 integumentary fin. Anterior end of the body provided with setce 

 and corneotts jaws. No foot-tubercles. Sexes united in the same 

 individual. 



This class includes only the singular pelagic animals belong- 

 ing to the genus Sagitta, the precise systematic position of 

 which is somewhat doubtful. They appear, however, to form 

 a connecting link between the Annelides on the one hand, and 

 the free Nematoids on the other hand. 



The Sagitta (fig. 134) have elongated transparent bodies, 

 rarely over an inch in length, having the hinder end of the 

 body expanded into a striated caudal fin, similar fins often 

 existing on the sides of the body as well. The head car- 

 ries a series of setae placed in front of the mouth, and the 



