672 



VERMES— CLASS ANNELIDA. 



Nearly all the species are marine, and many of them are of considerable 

 size and great beauty. According to structure and mode of life, they are 

 divided into two sub-orders— (1) the Sedeniakia or Tobicola and (2) the 

 Eeeantia. 



The typical membsrs of the Sedentariahve 

 in tubes of sand, mud, or pieces of shell glued 

 together by the slimy secretion of their skins, 

 or composed of a dense, shelly, chalk -like 

 substance. The worm known as Terebella 

 constructs a dwelling-place of the former 

 kind, gathering together the particles by 

 means of long flexible tentacles placed on 

 its head ; while tubes of cement are built by 

 such forms as Serpula and Spirorbis. The 

 latter is the maker of those tubes so much 

 resembling a snail-shell, which are common 

 on our coasts ; while Serpida makes the long, 

 sinuous, serpent-like tubes which may be 

 often found in interlacing clusters encrusting 

 stones and shells of various kinds. When 

 undisturbed these woims may be seen pro- 

 truding from their tubes and waving in the 

 water their gills and tentacles, which are 

 affixed to the head, but upon the slightest 

 alarm they shoot back like a flash out of 

 harm's way, and remain 

 securely concealed within 

 their homes until the danger 

 is overpast. To render it- 

 self still safer within its retreat, the worm called Serpula 

 has one of its tentacles transformed into a veritable 

 stopper, which exactly fits the mouth of the tube and 

 completely closes it up when the worm has withdrawn 

 itself. 



Although differing from the Serpula and Terebella, and 

 approaching the Errant Polychseta in many characters, the 

 common Sand-worm or Lug-worm {Arenicola marina), so 

 much sought for on our coasts as bait, also belongs to the 

 group of Sadentaria. In this species the gills are repre- 

 sented by plumes situated on the middle segments of the 

 body. At low water on the sandy shores of northern Europe 

 the Lug-worm may be found at times in great quantities, 

 the position of its burrows being easily detected by the 

 little heaps of sand that accumulate at the entrance. For, 

 like the Earth-worm, the Lug-worm swallows large 

 quantities of sand, in order to extract for its nourishment 

 any organic matter it may contain ; and it comes to the 

 suiface to unburden its body of the sand that has passed 

 through it. 



To the section Errantia belong the most highly-organised species of the 

 class. They lead a free predatory life, wandering hither and thither in 

 search of food, which consists almost exclusively of animals more defenceless 



Fig. 1.— TnBE-MAKiNO Annelid 



(Serpula contortxiplicala). 



a, Group of tubes with T,orm 



protruding. 

 &, Worm removed from tube. 



J'ig.2.— Lnfl-WOBM 

 (Arenicola marina\ 



