14 Papers from the Marine Biological Laboratory at Tortugas. 



to heat rays, for the worm gives no response to the more intense radiant 

 heat from a large dark area of heated iron. It is, however, sensitive to 

 light rays between the red and violet, and will respond to the light of a 

 two-candle-power incandescent electric lamp, the rays of which have 

 passed through a layer of carbon bisulphide 60 mm. in thickness, thus 

 filtering out the ultra-violet. 



As was demonstrated by Hesse, 1 in other Annelids, the anterior end 

 is most sensitive, the posterior end next, and the middle of the worm 

 least sensitive to stimuli. 



Solutions which consist of sodium, potassium, and calcium chlorides 

 are powerful initial stimulants, but finally produce depression of move- 

 ment and muscular tetanus in invertebrates. This deleterious effect can, 

 however, be overcome by adding magnesium to the solution, although 

 this destroys its stimulating properties. 



PART II. 

 CILIARY MOVEMENTS. 



Studies were made of the effects of various ions upon the ciliary 

 movements of fresh-water infusoria, vertebrate spermatozoa, Annelid 

 larvae, Veligers, Actinian larvae, and Ctenophorae. Among Annelid worms 

 I paid special attention to the trochophore larvae of the Atlantic palolo 

 worm, Eunice fucata, and of Spirobranchus tricornis and Pomatostegus 



c 



5 G 



FIG. 4. Above: Spirobranchus larvae 48 hours old. Below: Palolo larva*. A and C, side views. 

 B and D, oral views. Arrows show direction of movement. 



stellatus, all three of which may be obtained in abundance at Tortugas, 

 Florida. The trochophores of both Spirobranchus tricornis and Eunice 

 fucata rotate axially in the manner of a left-handed screw as they advance 

 in a sinuous path through the water. The rotation is in each case due 

 to the set of the cilia (see fig. 4). In stale sea-water or in magnesium 



1 Hesse, 1896, Zeit. fur wissen. Zool., Bd. 61, pp. 393-419. 



