404 F. W. GAMBLE AND FREDERICK KEEBLE. 



blackened bell-jar admitting light tlirougli a small "window." 

 The windows of these four covering bell-jars admitted 

 respectively white, green, red, and blue light. The windows 

 w^ere made by combinations of gelatine films, so selected as 

 to give, when tested b}?^ a hand-spectroscope, approximately 

 monochromatic light. The fifth cover admitted no light. 



Text-fig. 2, Series 1, shows the dispositions of Convoluta 

 when subjected to these light conditions. As is seen from 

 these figures, white light and green light induce a positive 

 phototropism. Darkness and blue light produce no asymmetry 

 of arrangement; whilst in red light the animals either remain 

 irregularly distributed, or show some indication of negative 

 phototropism. Hence the rays which determine the positive 

 phototropism of Convoluta are not those which determine the 

 movements of plaiits. From this it would seem probable that 

 the phototropic movement o£ Convoluta is independent of 

 any influence which its green cells may bring to bear upon it. 

 It is, however, interesting to note that this utilisation of the 

 green rays makes for economy, for the green rays are just 

 those of which chlorophyll absorbs least, and with which it 

 can most readily dispense. Whether light induces its effect 

 by acting on peripheral nerve-endings, or in the eye-spots of 

 Convoluta, we have not determined. 



We will conclude our study of phototropism by a brief 

 reference to the behaviour of young and sectioned animals to 

 light. Just as, in animals divided transversely, the head 

 ends only are sensitive to gravity, so are they alone sensitive 

 to light. ^ Inasmuch as oviposition takes place just beneath 

 the surface of the sand, the tail-ends — which may be, as we 

 have already described, torn off in the process — remain below 

 the surface, and, decaying, serve to nourish a rich saprophytic 

 flora. 



Though young Convoluta are strongly, positively photo- 

 tropic, the just-hatched larva) are aphototropic. After a 



' Loeb (ISD'iaiid 1900) refers to a similar result in the case of Tliysa- 

 nozoon, and neillier tin's author nor Parker and Burnett (1S09) obtained a 

 differential effect with fresh-water planarians. 



