144 NEREIDiE. 



of eyes on the vertex : antennae two, median, supported by two large 

 biarticulate palpi : proboscis biarticulate, with two jaws : tentacular 

 cirri four on each side in unequal pairs : feet well developed, lobu- 

 lated, with a dorsal and ventral setaceous cirrus ; two of the lobes 

 armed each with one spine, and with a bifasciculate brush of com- 

 pound bristles, the terminal piece acicular in most, but in many of 

 the lower brush falcate : anal segment with two setaceous styles. 



The name Nereis was imposed by Linnaeus on a group of Anne- 

 lides which had an elongated vermiform body furnished with soft 

 well-developed appendages, and a head, eyes, and tentacula*. The 

 characters of the group were modified by Pallas and Miiller ; and 

 Cuvier made them more precise and restrictive, by which the Eunicse 

 were separated from it. Savigny, in adopting these as separate 

 families, gave to their peculiar distinctions a still more precise defi- 

 nition. 



Blainville, on the contrary, reunited the families Nereides and 

 Eunices, and under the former name embraced a large number of 

 genera. These were divided into four tribes upon arbitrary prin- 

 ciples and distinctions, and the consequence is, that we find genera 

 which are much alike placed far asunder, while others no way nearly 

 allied are forced into almost juxtaposition. Even species of the 

 same genus are made members of different tribes. 



Audouin and M. -Edwards have followed much the same method 

 as Savigny, separating, however, from the Nereides some annelidans 

 whose structure seems to be too diverse. They retain in the family 

 all the Nereids of Savigny which have a distinct head, a large pro- 

 boscis generally armed with jaws, and a very considerable complexity 

 of exterior organization. 



The body of the Nereides is always slender, linear, and more or 

 less cylindrical. The number of constituent rings is in general very 

 considerable ; and, with a few exceptions, the rings which follow the 

 head are the largest, diminishing almost insensibly as they proceed 

 to the tail. Sometimes the body is narrowed towards both extre- 

 mities. The head is commonly of easy detection and indisputably 

 defined, but very variable in form. It is rarely without tentacula 

 and antennae ; and eyes are placed on its dorsal aspect. The pro- 

 boscis is a powerful organ, in general divisible into a basal and ter- 

 minal portion, and almost always armed with horny falcate cutting 

 jaws, denticulated like a saw along the inner margin. But in some 

 species the proboscis has no maxillae ; and yet this annelid may be 

 a member of a genus whose species are generally so furnished. 



In the great majority of the Nereides there are on each side of the 



* The last definition Linnaeus gave to Nereis is — " Corpus repens, oblongum, 

 lineare. Tentaculis lateralibus penieillatis. Os terminale unguiculatum. Ten- 

 taculis plumosis supra os." — Syst. p. 1085. This is less true than the previous 

 definition : — " Corpus oblongum, lineare, segmentis annularibus. Tentacula late- 

 ralia ad singulum segmentum utrinque solitaria. Os terminale unguibus duobus 

 arcuatis oppositis." — Syst. edit. 10. p. 654. 



