MOLLUSKS. 297 



be presumed, are directly connected with the act of repro- 

 duction, or with the development of the ova. 



The Gasteropoda, though capable of locomotion and 

 furnished with imperfect eyes, do not appear to be endowed 

 with sufficient mental powers for the members of the same 

 sex to struggle together in rivalry, and thus to acquire 

 secondary sexual characters. Nevertheless with the pul- 

 moniferous gasteropoda, or land-snails, the pairing is pre- 

 ceded by courtship; for these animals, though hermaphro- 

 dites, are compelled by their structure to pair together. 

 Agassiz remarks:* " Quiconque a eu 1'occasion d'observer 

 les amours des Unions, ne saurait mettre en doute la 

 seduction deployee dans les mouvements et les allures qui 

 preparent et accomplissent le double embrassement de ces 

 hermaphrodites." These animals appear also susceptible of 

 some degree of permanent attachment ; an accurate 

 observer, Mr. Lonsdale, informs me that he placed a pair 

 of land-snails (Helix pomalia), 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 communicated 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 Molluska, the Cephalo- 

 poda, or cuttle-fishes, in which the sexes are separate, 

 secondary sexual characters of the present kind do not, as 

 far as I can discover, occur. This is a surprising circum- 

 stance, as these animals possess highly-developed sense- 

 organs and have considerable mental powers, as will be 

 admitted by everyone who has watched their artful endeav- 

 ors to escape from an enemy, f Certain Cephalopoda, how- 

 ever, are characterized by one extraordinary sexual charac- 

 ter, 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 inde- 

 pendent life. So completely does the cast-off arm resemble 

 a separate animal, that it was described by Cuvier as a para- 



* " De 1'Espece et de la Class," etc., 1869, p. 106. 

 f See, for instance, the account whicli 1 have given in my " 

 nal of ttesearclies," 1845, p. 7. 



