1918] Essenherg: Distribution of the Polynaidae 215 



luents show such marked differences that they appear more like differ- 

 ent species than individuals of the same species. 



It is generally known that of the cosmopolitan polynoids occupying 

 different latitudes, the arctic examples as a rule are larger in size 

 than are those of the temperate or subtropical zones. Lepidonotus 

 squamattis exhibits a characteristic difference in size among indi- 

 viduals from different localities. Comparing the specimens of that 

 species from Finmark, New England, Puget Sound and from the 

 coast of California, great differences in size appear. The size of the 

 specimens from the coast of California is about one-third of that of 

 the specimens from Finmark and New England. The specimens from 

 Puget Sound are considerably larger than are the Californian but 

 they are inferior in size to the arctic and eastern forms. Ehlers 

 (1875) found also that the deep water forms were considerably 

 smaller and that they have thinner elytra. A further influence of the 

 depth on the polynoids is seen in the lack of pigmentation and the 

 eyeless condition of the worms. A great number of the deep water 

 polynoids are without eyes. Moore (1910) enumerates eight blind 

 deep water species of Polynoidae on this coast. Of all the numerous 

 polynoids in this collection, however, not a single specimen of the 

 littoral species of this coast is eyeless. Ehlers (1875) believed that 

 it is natural for the deep water annelids to be blind since many of 

 the deep sea species have been found in that condition. He accounts 

 for the possibility of some deep water individuals having eyes as due 

 to the yearly migration of littoral forms toward greater depths. 



The influence of the environment on the organisms is here very 

 marked. Considering the environmental differences in shallow and 

 deep oceanic waters, one will naturally expect to find the correspond- 

 ing physical changes in Polynoidae. Besides the minimum food con- 

 ditions in the great depths and the different chemical composition of 

 the water, the pressure in great depths is very much greater than in 

 the shallow waters, for it is a well known fact that the pressure in 

 the ocean increases by about one atmosphere for every ten meters in 

 depth; consequently in a depth of about 2,000 meters (1,000 fathoms) 

 there is a pressure of 200 atmospheres. It has also been proved by 

 various hydrographers (e.g., Murray, 1912) that there is no light in 

 the oceanic depths below 500 fathoms. On the brightest day and in 

 the clearest and most transparent waters only slight traces of the 

 blue light rays are perceptible at a depth of 1,000 meters. The green 

 rays are absent at a deptli of 500 meters, the red rays are absorbed by 



