222 Vniversitij of California Publications in Zoology [Vol. 18 



The greatest number of polyuoids is found in the littoral zones. The 

 number of polynoids decreases with the increase in depth. On the 

 other hand, a greater uniformity prevails among the littoral poly- 

 noids. The number of genera and species increases with the increase 

 in depth so that the deep water genera of this coast are almost two 

 times the number of the littoral, and the deep water species are almost 

 equal to the number of the littoral. This condition seems to indicate 

 that the littoral zone is the center of origin of the Polynoidae and 

 that they have migrated or have been driven occasionally from the 

 littoral zones to the deep water where they have probably under- 

 gone considerable external changes, forming thus new genera and 

 species, while the shallow water forms living in the same environment 

 have maintained a greater uniformity. Moreover, the different 

 environment in the greath depths, as the low temperature, the absence 

 of light, the difference in chemical composition of the water, may 

 produce a semipathologic condition in the polynoids affecting the 

 germ cells, and thus bring about rapid changes and partial degenera- 

 tion. This is suggested by the great degenerative changes found in 

 the deep water polynoids. The deep water species, as compared with 

 the littoral species, are as a rule smaller in size, and have delicate 

 cuticle and elytra. A great number of the deep water species are 

 without eyes. On this coast out of fourteen abyssal species eight are 

 known to be without eyes (Moore, 1910). This shows that the deep 

 water species have undergone certain physiological and morphological 

 specialization in adapting themselves to their particular environment. 

 This special adaptation or the degenerate condition, however, makes 

 them unfit to adapt themselves to any other environment. The low 

 temperature in the depths of the ocean undoubtedly has a great effect 

 upon the developing annelid eggs in producing abnormalities and 

 physical variations. This assumption is in accord with the laboratory 

 experiments where abnormalities, such as blindness and other defects, 

 are produced artificially by subjecting eggs in their early stages of 

 development to a low temperature. Secondly, the embryos may be 

 affected by the sudden environmental changes or by the shock effect 

 of the sudden change of temperature. The annelid trochophores 

 rising from great depths to the surface would naturally come sud- 

 denly into a very much higher temperature which would kill the 

 majority of them or would modify them greatly. In the littoral zones 

 where the difference between the bottom and surface temperatures is 

 less conspicuous, the worms in their embryonal development are not 



