ANNULATA. 231 



antly in the sand and mud of harbors, amid the vegetation of the bottom, 

 and over exposed objects of all sorts from low water mark to unknown 

 depths. Their value in utilizing debris and the more minute organisms 

 as food and thus becoming a link in the saving of these to serve as food 



FIG. 105. 



FIG. 105. Amphitrite ornata, from Vert-ill's " Invertebrate Animals of 

 Vineyard Sound." 



for the higher organisms cannot be over-estimated. (Figures 105 and 106.) 

 Subclass II. Oligochcsta {with few bristles). These are Chaetopoda 

 with no parapodia and comparatively few setae which usually occur in 

 two or four clusters in each segment. They are mostly fresh water or 

 terrestrial in habit. Fleshy outgrowths, such as gills, are almost uni- 

 versally absent. The sexes are united in one individual and the accessory 

 reproductive organs are very complicated. Ovaries and testes limited 

 to a small number of anterior segments ; development direct. The head 

 riot so highly specialized as in the Polychseta. 



The earthworms, of which there are numerous species, are the best 

 known types of this subclass. The genera and species are distinguished 

 chiefly by the position of the sexual organs. The aquatic Oligochaeta, 

 which are much smaller, are found in practically all ponds and ditches 

 where organic, matter is decaying. The more common genera are Dero 

 (Fig. 99), a beautiful, almost transparent worm which often forms a tem- 

 porary tube for itself of particles cemented by its own secretion, and 

 Tubifex, a longer worm which burrows in the mud at the bottom of 

 streams ; a portion of the body protrudes from the mud and waves gently 



