1? 



The Nautilus. 



Vol.. XXI. NOVEMBER, 1907. No. 7. 



EYES OF HELICODISCUS LINEATUS. 



BY EDWARD S. MOUSE. 



Last year in studying the eyes of the smaller Helices I discovered 

 that Helicodiscus lineatus was destitute of any pigmental organ 

 functioning as an eye. A further examination with a higher power 

 reveals apparently rudiments of a structure which may indicate the 

 traces of an eye but not the slighest evidence of pigmentation was 

 seen. The body and tentacles are a clear white. 



In the volume on Mo Husks in the Cambridge Natural History 

 series the Rev. A. II Cooke gives an interesting resume of what is 

 known of the molluscan eye. He says, " In land mollusca which 

 live beneath the surface of the ground or in absolute darkness the 

 eyes are generally more or less modified. Thus in TestnceUa, which 

 usually burrows deeply in the soil but occasionally emerges into the 

 open air, the eyes are very small, but distinct and pigmented. Oar 

 little CaecilinneUa acicula, which is never seen above the surface, is 

 altogether destitute of eyes. A species of Zospewn, a Helix and a 

 Bithynella from dark caves in Carniola bave suffered a similar loss." 



The habits of H. lineata do not differ apparently from the other 

 smaller species with which it is associated. I hope later to make 

 some experiments in phototaxis. 



