ANNULATA 



237 



stock in that it is sexual. Amphitrite is a beautiful worm which represents the 

 attached or tube-forming types. As the result of their habits such forms tend to 

 lose their segmentation and the appendages of the posterior part of the body. The 

 gills and tentacles accumulate about the head. These and other types grow abun- 

 dantly 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 for the higher organisms cannot be 

 overestimated. (Figs. 107 and 108.) 



Subclass II. Oligochata (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 



FIG. 108. 



FIG. 108. Cirratulus grandis, from Verrill. 



Questions on Figs. 107 and 108. Are these Chaetopods? What are your 

 evidences? What is the nature and function of the numerous outgrowths (bran- 

 chial cirri)? In what respects are they differently arranged in the two types? 

 Are these Oligochaeta or Polychasta? Your reasons? 



outgrowths, such as gills, are almost universally absent. The sexes are united in 

 one individual and the accessory reproductive organs are very complicated. Ova- 

 ries and testes limited to a small number of anterior segments; development 

 direct. The head not so highly specialized as in the Polychaeta. 



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 



