ARICIID^E. 



495 



of deeply stained nuclei occur below the cords. The oblique muscles are attached to the 

 upper arch, to the middle of which the gut is fixed by strong converging muscular fibres, 

 so different from the usual lax band attached first to the ventral vessel and then to the 

 arch of the cords. 



Audouin and Milne Edwards regarded the genus Arid a, Savigny, as intermediate 

 between the Errant Annelids and the Tubicola, and also possessing certain modifications 

 of structure found in the Terricola. 



Their bodies are long, flattened dorsally and rounded ventrally, with numerous 

 segments. Head small, conical, of one segment, devoid of appendages. The proboscis 

 is unarmed. From the second segment backward are feet, the first twenty or thirty 

 having two divisions which differ from each other, whilst the subsequent feet have 

 divisions resembling each other and dorsal in position. 



(Ersted 1 (1844), grouping the Annelids under three great divisions (his orders), viz., 

 Maricolae, Tubicolee, aud Terricolse, further subdivided the Maricolaa into the Chsetopoda, 



(S^ffiMffii 



m 



Fig. 94. — Highly magnified view of the nerve-area in Aricia Latreillii towards the middle of the body. The hypoderm and 



cuticle are below. 



which he split into the G. trematodina, G. vera, and G. terricolina, the family Ariciae 

 constituting the second of the last section. He characterized them as having a somewhat 

 rounded body of a definite number of segments, a simple alimentary canal without maxillge, 

 and a head with rudimentary appendages. But his family contained diverse forms now 

 included under several families, and those dealt with here fell under his Aricias verse, 

 in which the pinnae and branchiae are dorsal, and the tentacular appendages absent or 

 rudimentary. 



Grube 2 chiefly followed the arrangement of (Ersted in his tenth family Ariciea, Aud. 

 & Edw., grouping the Spionidas, Sphaerodoridas, and Cirratulidas as well as the Ariciidas 

 under this heading, but he separated the Opheliidde. 



Dr. Thomas Williams 3 observes that the segmental organ is very prominent in this 

 group, though limited to the two posterior thirds of the body. The ova and sperm- 



1 ' Arch. f. Naturges./ Bd. x, p. 102. 



2 < Fam. der Anriel./ p. 64, 1851. 



3 < Philos. Trans./ 1858, p. 125, pi. vii, fig. 17. 



