68 



ANIMAL FORMS 



to the belief that the ancestors of some of these animals 

 were segmented worms whose present condition has arisen 

 possibly in accordance with their sluggish habits. This 

 view is strengthened by the fact that in a very few species 



the- larvae are dis- 

 tinctly segmented, 

 but lose this char- 

 acter in becoming 

 adult. As before 

 mentioned, the 

 greater number of 

 species live in bur- 

 rows in the sand 

 or crevices in the 

 rocks, from which 

 they reach out and 

 gather in large 

 ^quantities of sand. 

 As these substances 



FIG. 42. Agephyrean worm (Dendrostoma). Specimen pass down the in- 

 on left opened to show k, kidney, m, muscle bands, , , . ,, 



and .., nerve-cord. testme the niltri- 



tive matters are di- 

 gested and absorbed, while the indigestible matters are 

 voided to the exterior. When large numbers are associated 

 together they are doubtless important agents in modifying 

 the character of the sea bottom, thus acting like the earth- 

 worms and their relatives. 



71. The sea-mats (Polyzoa). The sea-mats or Polyzoa 

 constitute a very extensive group of animals common on 

 the rocks and plants along the seashore, and frequently 

 seen in similar situations in fresh-water streams. A few 

 lead lives as solitary individuals, but in the greater number 

 of species the original single animal branches many times, 

 giving rise to extensive colonies. In some species these 

 extend as low encrusting sheets over the objects on which 

 they rest; while in others the branches extend into the 



