AMPHARETIDAE. 441 



or proboscis-like tube (Pabits). In some forms the tentacles are wholly absent. 

 The eyes are two, or numerous. Nuchal organs are present either as simple» 

 nonextrusible, ciliated furrows or as pits surrounded with a ridge, or cushion. 



Ventral glands are strongly developed and normally form obvious cushions 

 extending entirely across the somites of the thoracic region. 



The first parapodia appear normally on the fourth somite, where they are 

 often reduced and bear weakly developed setae. Simple setae may be present 

 also on the second and third somites, e.g., in Melinna. The parapodia of the 

 thoracic region, excepting in most cases a few of the most anterior ones, are 

 biramous, with the notopodium prominent and cylindrical or conical, while the 

 neiu'opodium is in the form of a pad, or lamina, the torus, or pinnule. The first 

 uncini begin in most cases on the sixth or seventh somite, but may begin on the 

 fourth at the same time as the notopodials. In the abdominal region, in the great 

 majority of cases, only the neuropodia, or pinnules, are present; but, in some^ 

 achaetous tubercles may be present above these, and the tubercles more rarely 

 may bear capillary setae to the end of the body. Cirri absent, or of variable 

 development. 



The setae are of two types. The notopodials are capillary, simple, and 

 laminate. The neuropodials are in the form of minute pectinate plates, or 

 uncini, much resembling those of the Terebellidae. In addition, a third type of 

 seta is present in certain genera. These are the stout blades, or paleae, that 

 may form two transverse series on the third somite. They are really the dorsal, 

 or notopodial, setae of that somite, the parapodia being represented only by the 

 tubercles, or ridge, from which the paleae arise on each side. 



One or two stout spines, or hooks, may be present on each side of the dorsum, 

 just behind the branchiae. 



There may be two, three, or four pairs of branchiae, four pairs being the 

 most common number. They are inserted dorsally, with the first pair on the 

 third somite, a pair also being present on each following somite to the sixth, 

 inclusive, when the full number, or four pairs, are present. The branchiae are 

 nearly always smooth, distally acuminate, and unbranched, or they may all or 

 part of them be branched. 



The nephridia occur in the thoracic region and number from three to five 

 pairs, the first lying normally in the fourth or fifth somite back of an intrathoracic 

 diaphragm, which divides the thoracic cavity unequally. They open into the 

 body-cavity, and the external opening, or nephridiopore, is in each case situated 

 at the base of the corresponding neuropodium. 



