296 NATURAL SCIENCE [November 



this inspection might well, we should suggest, be assumed by the 

 various Sea Fisheries Committees around the coast. 



The Method of Feeding of Helix hortensis 



Mk E. Eathay publishes an interesting article on the method of 

 feeding of Helix hortensis, in the third part of Vol. viii. of the 

 Zeitschrift fur Planzenhrankheiten. 



The author had noticed on the smooth bark of ash-trees certain 

 undulating patterns, in the immediate neighbourhood of which, or 

 at their extremities, were individuals of Helix hortensis. Mr Rathay 

 therefore felt that the patterns must be accounted for by the snail's 

 method of feeding. 



To make certain of the fact, he took some bits of ash-bark on 

 which no patterns had been traced, set them in an upright position 

 so as to keep them fresh in the water, put a Helix on each, and 

 covered them over with a glass bell. The very next day, these bits 

 of bark showed traces of undulating patterns. 



In consequence of this experiment, the author's attention was 

 drawn to other smooth-barked trees, and he recognised the same 

 patterns on Salix caprca L., S. amygdalina L., Alnus incana C, &c. 



These traces were noticed on the trunks to the height of 7 to 

 9 metres, and the snail that was observed to be at work, produced 

 them by slowly advancing his body and swaying his head alterna- 

 tively to right and left. 



One might suppose that the gasteropod fed himself thus by 

 gnawing the bark of the tree, but it is nothing of the kind ; he 

 attacks the spots where the bark is powdered with a small alga, 

 Pleurococcus vulgaris, Menegh., and scarcely touches the outer skin 

 of the bark. 



In fact, in the excrement of Helix hortensis are found the cells 

 of Pleurococcus almost intact. 



In accordance with the experiments detailed in the note and 

 after the employment of various appropriate reagents, it is recog- 

 nised, not only by microscopic examination, but by chemical experi- 

 ment, that the cells of Pleurococcus have been evacuated intact with 

 their chlorophyl. 



The author's conclusions are as follows : — 



1. It is only on smooth barks sufficiently coated with alga that 

 the undulating patterns can be detected. 



2. It can easily be observed, especially on the older trees, that 

 Helix hortensis does not eat the outer skin of the bark and scarcely 

 touches it. 



3. The excrement of the same gasteropod, taken a great height 

 up the tree, is chiefly composed of cells of Pleurococcus with 

 very few fragments of periderm is. The extraordinary thing about 



