210 University of California Pahlications i)i Zoology [Vol. 18 



750 fathoms, a depth which is the zone of an optimum temperature for 

 the group. Below 750 fathoms they undergo semipathological changes, 

 forming new genera and species. Murray (1898) suggests that the 

 ancestors of the fauna of great depths have migrated from many shal- 

 low water areas, hence the great diversity of genera. This would 

 hardly be necessary. If by sudden change in temperature different 

 kinds of beetles can be produced (Tower, 1906), and if changes in 

 temperature or treatment with potassium cyanide or magnesium sul- 

 phate can produce abnormal fish (Loeb, 1915; Stockard, 1909), it 

 seems entirely possible that chemical and physical agents in the depths 

 of the oceans may affect the deep water fauna in such a way as to 

 modify their external appearance to so great an extent that in time 

 the new generations are quite unlike their sliallow water ancestors and 

 become new species. The great number of genera and species of deep 

 water Polynoidae may have been produced by the action of the chemical 

 and physical influences upon migrants from the littoral zone. 



A further proof that similar chemical and physical conditions may 

 produce similar results affecting organisms equally is the fact that 

 identical species of aquatic animals are found in corresponding life 

 zones on both sides of the equator. Murray (1898) enumerates 150 

 identical species of Metazoa, and about 100 closely allied species, occur- 

 ring in the extra-tropical regions of the northern and southern hemi- 

 spheres, which are wholly unknown from the intervening tropical belt. 

 This phenomenon suggests that similar chemical and physical condi- 

 tions have a tendency to produce similar results. Furthermore, it is 

 a generally known phenomenon that chitinous and calcareous animals 

 are abundant in the tropics, while animals secreting little or no lime 

 salts or chitin are more abundant in polar regions and in great depths. 

 The deep water Polynoidae of the Pacific Ocean have soft, thin scales 

 and cuticle. This condition may have been produced by chemico- 

 physical influences which arise in the colder waters in the depths. 



VI. Food Habits and Mode of Life 



Polynoidae are voracious feeders, devouring any animal they can 

 capture. Their chitinous jaws are strongly developed and well adapted 

 for their purpose. In captivity they attack one another, severing seg- 

 ments and scales from the bodies of their companions ; hence it is 

 difficult to keep alive a number of Polynoidae in the same aquarium, 

 for they inflict such serious harm to one another that they soon die. 



