SIBOGLINUM EXILE 



311 



0.1 



MM 



I 



3 





ш 



ш 





D 



The tube of 5. exile is thin, brown, 

 elastic, lustrous and thin-walled. In 

 front it is fibrous. It is unsegmented 

 but ringed and there are very charac- 

 teristic double rings in the middle part 

 of the tube. A considerable length of 

 the anterior end of the tube is trans- 

 parent and colourless, with soft flimsy 

 walls. Then follows a still colourless 

 but fibrous part. Brown rings gradually 

 appear, forming from local accumula- 

 tions of transverse fibres. The inter- 

 spaces between the rings are large and 

 clear, but still fibrous; they are half as 

 long as the tube is wide, and the rings 

 are only half this — a quarter the dia- 

 meter of the tube (Fig. SSI 33/4). Then, 

 a little farther back (but still in the 

 anterior part of the tube), the rings be- 

 come denser and darker, remaining, as 

 before, fibrous. In this region they are 

 a third to a half as long as the dia- 

 meter of the tube. The interspaces are 

 narrow and clear (Fig. SS133Z?). A 

 considerable region in the middle of the 

 tube is characterized by double rings. 

 In general the length of each doublet, 

 taken as a whole, is about a quarter 

 the diameter of the tube, and the inter- 

 spaces are the same length. The fibrous 



nature of the rings here disappears and the colour is golden-brown (Fig. 

 SS133C). In the hind part of the tube the double rings are preserved, but 

 both the rings and the interspaces are longer, and the strict regularity of the 

 rings disappears (Fig. SS133D). The very longest tube is 85 mm, the anterior 

 diameter is 0-135 mm and the posterior 06 to 0-09 mm. 



S. exile has much in common with a whole series of species, including 

 the possession of a bipectinate tentacle, three girdles, and a strongly de- 

 veloped anterior tooth-group on the platelets of the girdles. It is distin- 

 guished from all such species, however, by the oblique cuticular rodlets of 



Ш 



'ЗШЕ 



Fig. SS133. Siboglinum exile: 



A-D - successive portions of the tube. 



