PHYLUM ANNULATA 



noio 



neuro 



vent.cirr 



dorsal cirrus : neitro. neuropodiuru ; noto. noto- 

 podium ; cent. cirr. ventral cirrus. (After 

 Claparede.) 



short cylindrical tentacles (tent), and further buck a pair of 

 somewhat longer stout appendages or palpi (palp). The peri- 

 stomium, which has some 

 resemblance to the seg- 

 ments of the body, though 

 wanting the parapodia, bears 

 laterally four pairs of long, 

 slender, cylindrical tentacles 

 (perist. tent) : on its ventral 

 aspect is a transversely 

 elongated aperture, the 

 mouth. The segments of the Ku , :!r);} _ Nereis dumeriui . A sil , Ble ,,,,,,. 



body differ little in external podium, magnified : tic. adciilum ; dors. cirr. 



characters from one another 

 throughout the length of the 

 worm. Each bears laterally a pair of parapodia, which in the 

 living animal are usually in active movement, aiding in creeping, 



or acting as a series of oars for propelling it 

 through the water. When one of the parapodia 

 (Fig. 353) is examined more attentively it is 

 found to be biramous, or to consist of two dis- 

 tinct divisions a dorsal, which is termed the 

 notopodium (noto), and a ventral, which is called 

 the neuropodium (neuro). Each of these is 

 further subdivided into several lobes, and each 

 bears a bundle of setse. Each of the bundles 

 of setas is lodged in a sac formed by invagina- 

 tion of the epidermis the setigerous sac and is 

 capable of being protruded or retracted and 

 turned in various directions by strands of 

 muscular fibres in the interior of the para- 

 podium. In each bundle there is, in addition 

 to the ordinary setse, a stouter, straight dark- 

 coloured seta (ac.), the pointed apex of which 

 projects only a short distance on the surface ; 

 this is termed the aciculum. The ordinary seta3 

 (Fig. 354) are exceedingly fine, but stiffish, 

 chitinous rods, of which two principal kinds are 

 recognisable : both have a terminal blade arti- 

 culating with the main shaft of the seta by a 

 distinct joint ; but in the one variety the shaft 

 of the seta is finer than in the other, and the 

 (Alter terminal blade long, slender, and nearly 

 straight, whereas in the other variety it is 

 short and slightly hooked. On the dorsal side of the parapodium 

 is a short cylindrical, tentacle-like appendage, the dorsal cirrus 

 (Fig. 353, dors, cirr), and a similar, somewhat shorter appendage, 



magnified. 



Claparede). 



