220 



LOWER INVERTEBRATES. 



movable like a limb and each having at the end a cluster of many bristles, often of 

 bizarre shapes and brilliant shades of color. 



Oedbr I. — OLIGOCH^TA. 



The Oligochaeta are all hermaphrodites, are without cephalic appendages, and have 

 no armature around the mouth. The best known of the order, and indeed of the 

 whole class of Annelida, is the familiar earth-worm, the favorite victim of an art 

 which serves to lure boys to brooks, and to betray fishes into the frying-pan. We 



owe to Darwin a series of 

 most interesting observa- 

 tions on the habits of earth- 

 worms, and the role they 

 play ill the economy of 

 nature, and we are almost 

 equally indebted to the 

 acute studies of Von Hen- 

 sen. The characteristics 

 of earth-worms are, the ab- 

 sence of appendages, the 

 large number of small seg- 

 ments, the small size and 

 number of the bristles, the 

 want of sense organs, and 

 the development of a belt 

 or clitellus ; this is a thick- 

 ened portion of the body, 

 not far beliind the head, 

 and having a smooth, glis- 

 tening surface. 



Xiumbricus terrestris is 

 common botli in Europe 

 and America. I quote 

 Linnaeus' description as 

 given in Turton's quaint 

 translation : " Inhabits decayed wood and the common soil, which by perforating it 

 renders fit to receive the rain ; devours the cotyledons of plants and wanders about by 

 night ; is the food of moles, hedgehogs, and various birds. Body with about one 

 hundred and forty rings, each of which contains four pair of prickles, not visible to the 

 eye but discoverable by the touch ; when expanded is convex each side, and when 

 contracted is flattish beneath, with a red canal down the whole body ; the belt is 

 wrinkled and porous ; mouth placed beneath the proboscis." N"ow this description 

 is altogether inadequate for the discrimination of the species, nevertheless we will let 

 it pass ; still less satisfactory are the remarks on the habits, which we must amend and 

 extend. First of all let us add that "belt" means the clitellus, which in this species 

 includes six segments, so fused that the external demarcations are obliterated. 



Earth-worms are essentially burrowing animals, nocturnal in their habits, although 

 they sometimes leave their holes and crawl over the ground to a new locality, and also 



Fig. 211. — Parapodia of Htteroitcrtis , c, upper, g, lower divisions. 



