ANNULOSA I ANNELIDA. 



215 



tubercles are developed. The ciliated band or bands finally 

 disappears, and new rings are rapidly added by intercalation 

 between the head and the segments already formed. 



Amongst the best known of the Errantia is the common 

 Lob-worm (Arenicola piscatorum, fig. 81, C), which is used by 

 fishermen for bait. The Lob-worm lives in deep canals which 

 it hollows out in the sand of the sea-shore, literally eating its 

 way as it proceeds, and passing the sand through the alimen- 

 tary canal, so as to extract from it any nutriment which it may 

 contain. It possesses a large head, without eyes or jaws, and 

 with a short proboscis. There are thirteen pairs of branchiae 

 placed on each side in the middle of the body. 



Fig. 81. Errant Annelidas. A, Hairy-bait (Nephthys) ; B, Sea-mouse (Aphrodite]: 

 C, Lob-worm (A renicola). (After Gosse.) 



In the Nereidce, or " Sea-centipedes," the body is greatly 

 elongated, and consists of a great number of similar segments, 

 with rudimentary branchiae. The head is distinct, and carries 

 eyes and feelers, whilst the mouth is furnished with a large 

 proboscis, and often with two horny jaws (fig. 80). 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. 



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 



