THE EVIDENCE OF SNAILS. 



285 



It is obvious that animals with feeble powers of travel are of the 

 greatest value in these researches, because they indicate more ancient 

 and more enduring changes of sea and land than freely mobile crea- 

 tures, such as birds and quadrujDeds, which may spread, conditions 

 favoring, with great rapidity. Moreover, the invertebrates have changed 

 much more slowly than higher animals; their evolution has been slow. 

 Almost the whole great drama of mammalian evolution has been acted 

 during Tertiary time, while there has scarcely been generic change in 

 the mollusks ! Mammals and birds reflect in their distribution the later 

 earth movements, the invertebrates and fishes the earlier. 



The Helix snails are particularly well adapted to show ancient 

 faunal relationships, as they occur under one or another form in almost 

 all lands. But it is only in the present decade that their anatomy has 

 been understood, and the true relationships of the various groups of 

 the family recognized. One of the most interesting developments of 

 the anatomical study of land snails has been the demonstration of a 

 close relationship existing between Helices of the Philippine Islands 

 and eastern Asia and those of California, Mexico and the Greater 

 Antilles. 



Years ago Dr. Karl, Semper, in his Travels in the Philippine Archi- 

 pelago, showed that the arboreal Helices of the Philippines are pro- 

 vided with a muscular sack containing a calcareous needle — the so- 

 called ^dart' — and surmounted by a mucous gland, the whole being 



\ TYiucoasglondL 

 clartyiack 



1. Dart Apparatus of Epiphragmophora mormonum, a Californian Snail. 



2. The Dart, Enlarged. 3. Do. of Chlor^a benguetensis, Phillippines. The Position 



OF the Dart in its Sack is shown by Dotted Lines. 



an appendage of the reproductive organs. In species of both China 

 and Japan the same peculiarities are found in these organs. It was 

 already known that the Helices of Europe have a similar sack and dart, 

 but the associated mucous gland is split into finger-like tubes and re- 

 moved from the sack to an adjacent duct. The function of the dart 

 apparatus is not well understood. The snails thrust their darts into 

 one another during the mating time, and hence the dart is believed to 

 be an excitation organ. 



VOL. LIX. 19 



