ANATOMY AND PHYSIOLOGY OF A SNAIL. 19 



banded; others are unicolorous or banded. Mr. J. W. Taylor, 

 in his recent " Valedictory Address as President to the Concho- 

 logical Society for the year 1887," published in The Journal of 

 Conchology for April, 1888, makes the following statement : 

 " Nearly seven years ago Mr. Ashford suggested to me the proba- 

 bility that Helix cantiana, cartusiana, etc., were once banded 

 species, and I am disposed to agree with his suggestion." But 

 there seems to the writer scarcely any foundation for such a sup- 

 position, and he would disagree with such a statement for five 

 reasons. In the first place, the primary shell in the embryo of all 

 species is unicolorous ; in the second place, the youngest portion 

 (nucleus) of the secondary shell in all species is unicolorous ; in 

 the third place, unicolorous specimens are most common in aquatic 

 forms, where environmental circumstances have doubtless not 

 been so great as on land ; in the fourth place, of a banded species 

 unicolorous specimens are invariably found ; and in the fifth place, 

 such a supposition is not general and comparative enough. Thus, 

 the writer is inclined to the opinion that all the species of our land 

 and fresh- water mollusca were once, and only, unicolorous. What 

 the causa causans of the future banding was, we are, practically at 

 any rate, in doubt. It remains as one of Nature's greatest arcana 

 for the great future to solve. 



In H. nemoralis and H. hortensis the bands vary in number and 

 degree of development, so that it is necessary to have some 

 system by which we can represent these variations on paper for 

 the use of our fellow-workers. The system is known by the 

 name of the system of the band-formula. The type of each 

 species has five bands, which are represented by the figures 

 12345, the 123 referring to three bands above the periphery, and 

 the 45 to two bands below it. When a band is interrupted it is 

 shown by a colon, thus, 12:45 5 when slightly developed, by the 

 insertion of the figure representing that band below the line of 

 the others as 12345, when obsolete by a cypher, as 02345, or 

 ooooo ; and when two or more bands are fused together into one 4 

 band it is shown by bracketing the figures standing for the com- 

 ponent bands, thus, 123 (45), (123) (45). If more than five bands 

 be present the extra band is represented by the insertion of the 

 letter x into the formula, as 12 x 345 or i x 2345. 



