SI 6 SEXUAL SELECTION. [Part II. 



a pair of land-shells (Helix pomatia), one of which was 

 weakly, into a small and ill-provided garden. After a 

 short time the strong and healthy individual disappeared, 

 and was traced by its track of slime over a wall into an 

 adjoining well-stocked garden. Mr. Lonsdale concluded 

 that it had deserted its sickly mate; but after an absence 

 of twenty-four hours it returned, and apparently commu- 

 nicated the result of its successful exploration, for both 

 then started along the same track and disappeared over 

 the wall. 



Even in the highest class of the Mollusca, namely, the 

 Cephalopoda or cuttle-fishes, in which the sexes are sepa- 

 rate, secondary sexual characters of the kind which we 

 are here considering do not, as far as I can discover oc- 

 cur. This is a surprising circumstance, as these animals 

 possess highly-developed sense-organs and have consider- 

 able mental powers, as will be admitted by every one 

 who has watched their artful endeavors to escape from an 

 enemy. 2 Certain Cephalopoda, however, are characterized 

 by one extraordinary sexual character, namely, that the 

 male element collects within one of the arms or tentacles, 

 which is then cast off, and, clinging by its sucking-disks 

 to the female, lives for a time an independent life. So 

 completely does the cast-off arm resemble a separate ani- 

 mal, that it was described by Cuvier as a parasitic worm 

 under the name of Hectocotyle. But this marvellous 

 structure may be classed as a primary rather than as a 

 secondary sexual character. 



Although with the Mollusca sexual selection does not 

 seem to have come into play, yet many univalve and 

 bivalve shells, such as volutes, cones, scallops, etc., are 

 beautifully colored and shaped. The colors do not appear 

 in most cases to be of any use as a protection ; they are 



2 See, for instance, the account which I have given in my ' Journal 

 of Researches,' 1845, p. 7. 



