THE BRISTLE-WORMS. 



109 



Fio. 36. Foot, or 

 parapodium, of 

 Nephthys hom- 

 bergii. d, dorsal, 

 and v, ventral lobes 

 of foot with bristles 

 and thin plates, p ; 

 g, gill ; c, ventral 

 cirrus, the dorsal 

 is absent. After 

 Ehlers. 



being quadrangular in section. The dorsal surface is flat, 

 and so also is the ventral, save that it has 

 a very distinct median groove. The foot 

 is of remarkable structure (see Fig. 36). 

 When fully protruded the introvert is 

 seen to be furnished with numerous 

 papillae. There are also two jaws, but 

 these are small and are not protruded. 

 The worm is readily recognised by its 

 opalescent colours and its very active 

 movements, and is a common form which 

 ought to be found and studied. 



While digging for Nephthys one may 

 occasionally turn up an elongated worm 

 with a body which narrows rapidly in 

 the posterior region to form a long tail. 

 The colour is pale yellowish, and the 

 animal has an eminently characteristic 

 habit of coiling itself into a spiral on 

 the slightest touch. The head is extra- 

 ordinarily long and pointed. An animal 

 displaying these characters is a species of Glycera, and the 

 commonest species between tide-marks is G. capitata. In 

 most species there may be seen on the dorsal region of the 

 feet in the living worm, small sac-like gills in which the 

 blood corpuscles circulate rapidly, but these are absent in 

 G. capitata. The long introvert is crowned by four dark 

 jaws, which in the large Glycera of deep water (G. giganted) 

 are strong enough to pierce the skin. The different species 

 are distinguished by the presence or absence of gills, and 

 the minute structure of the parapodia. 



The most interesting point in regard to the habits of 

 Glycera is the strange way in which it throws the body 

 into a close spiral. Like most sand-inhabiting worms it is 

 not easy to keep alive in captivity. 



In the reduction of their tentacles, palps, and cirri, 

 Nephthys and Glycera lead up to the next genus we shall 

 consider. This is the genus Nerine (rag-worms), which 

 includes worms without any trace of palps or tentacles. 

 The peristomium bears a single pair of long tentacular cirri, 

 the dorsal cirri are converted into gills, and the ventral cirri 



