WOODWORTII: THE PALOLO WORM. 13 



out the ventral eye-spots are fully developed only in the posterior free- 

 swimming part of the Palolo. 



According to Riggenbach (1902) autotomy (Selbstverstiimmlung) in 

 annelids is brought about through external stimuli, and the parent 

 atokal part of the Palolo may be looked upon as a sexual nurse or stock 

 which regenerates the epitokal region, a process comparable to stabiliza- 

 tion in cestodes. Brunelli and Schoener (1905), who name this process 

 schizoepitokie, call attention to the fact that the most complicated re- 

 productive processes in annelids exist in those forms that inhabit shores 

 and reefs, are simpler in pelagic forms, still less complicated in fresh 

 water forms, and simplest of all in terrestial forms. In the phenomenon 

 of the periodic appearance of the " Palolo " they believe that inorganic 

 forces have played the most important part in establishing reproductive 

 autotomy, and since annelids inhabiting reefs and shores are subject 

 to wounds and amputations due to the action of the waves on rock- 

 fragments and sand, and friction between the worm and the rock, etc., 

 epitokie arose from such amputations, which later became simple division 

 and finally adapted to the dissemination of the species, and since these 

 mechanical causes were coincident with certain seasons, such a periodic 

 seasonal mechanical stimulus has played an important role in the an- 

 cestral history of the Palolo. 



The periodic swarming of the " Palolo " has been ascribed to various 

 stimuli such as light, heat, salinity and pressure of the water, atmos- 

 pheric electricity, etc. Friedlaender (1898), says that a reaction to light 

 has nothing to do with the " Palolo " phenomenon, neither moonlight, 

 which is reflected light, nor the light of dawn, and suggests a negative 

 geotropism through diminished water pressure at low tides. The 

 " Palolo " appears in the months of October and November in the last 

 quartering of the moon. This is the season of neap tides, when the reef 

 flats are uncovered or only awash. At this season the sun is nearest the 

 zenith in southern latitudes, a season when the sun's light and heat is 

 greatest. I believe in some heliotropic or thermotropic reaction of the 

 eye-spots borne on the segments of the epitokal part of the Palolo. A 

 glance at Text Fig. 2, p. 11, showing the structure of one of these ventral 

 eye-spots is more than suggestive that their function is to react in some 

 way to light or heat rays. Friedlaender's contention that the " Palolo " 

 appears in almost absolute darkness does not, to my mind, preclude a 

 reaction of the eye-spots to light or heat, for these influences have been 

 acting for a considerable period of time as there are three distinct days 

 involved in the l rising' of the " Palolo." 



