ON THE MORPHOLOGY OF THE NEPHRIDIA OF NEREIS LIMNICOLA JOHNSON

¹ Division of Worms, Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560

1. The morphology of the nephridia of specimens of the polychaete worm, Nereis limnicola Johnson from areas of different salinity in the estuary of the Salinas River is described.

2. Generally, the canal diameters of the nephridia of the up-river (low salinity) forms are larger than those from down-river (high salinity); the nephridia of the up-river forms are more highly vascularized than those from animals found in higher salinities. This suggests that the nephridial canal acts to rid the animal of the excess water brought into its body by osmotic influx.

3. Nephridial canal diameters of worms adapted from low to high and from high to low salinities approach those of the animals from low salinity; this suggests that a larger canal diameter is efficacious in coping with the osmoregulatory problems presented by a dilute medium, and that canal diameter is not very important in higher salinities.

4. Inconsistencies in the correlation of large nephridial canal diameter with low salinity suggest that other mechanisms are utilized in meeting the stresses imposed by an environment of low salinity.

5. Krishnamoorthi's Index of Excretory Capacity is derived for a number of nephridia; the results indicate that the Index and/or the nephridia of N. limnicola do not seem to be comparable with Krishnamoorthi's observations on polychaetes of India.