Converse Relation between Ciliary and N euro-Muscular Movements. 15 



solutions the larvae are often observed to swim in circles, as shown in 



fig- 5- When young, the trochophores of Eunice jucata often turn over 



end for end as they advance through the water. 



When placed in a flat Petri dish in the diffuse 



light of the laboratory the larvae of both these 



worms swim in all directions, at random, as is 



shown in fig. 6, which represents observed paths. 



When, however, larvae enter the light meniscus 



on the side toward or away from the window 



they exhibit the Jennings-reaction, as is shown 



within the dotted areas in fig. 6. They are thus 



trapped in locations of optimum light-intensity, 



not directed toward the light along the path of 



the rays. This applies not only to the larvae of the palolo but to Spir- 



obranchus and Pomatostegus. 



FIG. 5. Palolo larva "cir- 

 cling" in a magnesium 

 solution. 



FIG. 6. Paths of Palolo larvae in a Petri dish. 



It is remarkable that whatever the effects of the cations we are here 

 considering may be upon the neuro-muscular system, their effect upon 

 the movements of cilia are the exact opposite. 



EFFECTS OF SODIUM. 



A 0.6 molecular NaCl solution is a primary neuro-muscular stim- 

 ulant, but its effect upon the ciliary movements of Infusoria, worm- 

 larvae, Veligers, Semper's Actinian larva, and Ctenophorae is to derange 

 and inhibit without initial stimulation, so that ciliary movement ceases 

 usually in a few seconds, although in rare instances slight ciliary move- 

 ment may continue in this solution for 20 minutes. In other cases, 

 such as those observed by Prof. R. S. Lillie in Arenicola larvae and in 

 Mytilus, the cilia rapidly dissolve in NaCl. It is remarkable that while 



