400 NOTES AND MEMORANDA. 



and that it is more rapid in proportion as these succeed one 

 another more rapidly ; but these waves do not seem to be locomotive 

 when the animal is placed on a glass, as it was in Bergmann and 

 Leuckart's experiments, and the only change which then occurs is in 

 the coloration of the organ. So long as the animal is at rest, the foot 

 is all of the same colour, but when it begins to crawl the transverse 

 bands become darker {Helix, Avion), or of an ashy hue (Li max). In 

 Helix the waves pass over the whole of the foot anteriorly, and over 

 the great part of it posteriorly ; in Linv.tx and Avion they are limited 

 to the median third. 



Some three hundred experiments of the following character were 

 made : — A snail was made to crawl up a glass cylinder and the follow- 

 ing points were observed :—(l) The length of the animal; (2) the 

 length of the passage ; (3) the number of waves in an equal period of 

 time ; (4) how often a wave passed during the experimental period ; 

 (5) the length of the period ; (6) the weight of the body ; and (7) 

 the weight of the foot. Calculations based on these observations lead 

 to the conclusion that " the smaller animals have the greater power 

 of locomotion, and that tliis law does not apply merely to the smaller 

 genera and species, but also to the smaller and younger individuals of 

 the same species." It is, however, to be noted that in Helix pomatia 

 and HJwvtensis the waves succeed one another less rapidly in the smaller 

 than in the larger examples ; and it is concluded that the most suc- 

 cessful number of undulations are those of from 30 to 40 centimetres 

 in length. It follows from other measurements that the body moves 

 more rapidly up to a certain point, and that after this an increase in 

 the number of waves is of less use, while it is shown that the smaller 

 number of undulations in smaller animals is, within the limits of this 

 law, of greater physiological value than the higher number observed iu 

 the larger forms. The next law stated is now easily comprehensible — 

 the physiological value of the individual waves is inversely propor- 

 tional to the number of waves which pass over the foot in a given 

 period. From experiments in which the animals had a weight to 

 carry, it is found that within limits they are able easily to do so, in- 

 asmuch as the unloaded snails are not able to make use of all their 

 activity. 



The voluntary muscles of the Gastevoj)oda are those in the dermo- 

 muscular tubes, and those derived therefrom (m. columellaris, and 

 muscles of the tentacles) ; in formation these seem to be intermediate 

 between the smooth and the striped elements found in the Yevtehvata ; 

 these are the vetvactile muscles, by which the different j^arts of the 

 body are brought into relation ; while the pvotvusile muscles, or those 

 by which locomotion is effected, are the longitudinal muscular fibres of 

 the foot. In Helix these extend over the whole of the breadth of 

 that organ with the exception of a small marginal portion ; in Avioii 

 and Limax, as might be supposed from what has been already stated, 

 they are confined to the median third. In addition to these there are 

 other fibres which run in various directions, and there is a special layer 

 around the pedal gland, and above it there is a covering of transverse 

 muscular fibres ; in the upper half of the hinder portion there is a 



