PHOSPHORESCENCE. 247 



docs not proceed from browsing- on the plant, but from an 

 exhalation peculiar to the season of reproduction; and at the 

 same season the Ncgritae are as foetid as the goat.* Ano- 

 ther species of Helix (H. alliaria) smells at times strongly of 

 garlic. " When fresh taken," says Dr. Turton, " it diffuses 

 an odour exactly like the smell of garlic, so powerful that 

 two or three of them will scent a room for some hours ; "f 

 and, according to Mr. Sheppard, the collector may frequently 

 be guided to its retreat by this exhalation ; | so that what 

 Nature doubtless intended as a beneficial gift, will often 

 prove its bane in these evil days. 



8. Phosphorescence. — A luminous fluid is secreted by 

 several mollusca. Linnaeus tells us, on the authority of 

 Bartholinus, that, when the Octopus vulgaris is opened in 

 the dark, a light so strong and splendid is emitted, as per- 

 fectly to illuminate the room.§ The light is, however, 

 faint during life, and not general in the class. The Cleo- 

 dora is the only reputed phosphorescent species among the 

 Pteropods : and as for the Gasteropods, there is also amongst 

 them only one rival of the glow-worm. This is a slug (Phos- 

 phorax noctilucus), a native of the higher mountains in the 

 island of TenerifFe, distinguished by a small pore or disk 

 towards the posterior extremity of the shield, which is of a 

 glossy green in daylight, and luminous at night. || 



Of luminous bivalves there are also few examples. Bosc 

 instances the Solens, or Razor-fish ;^ and Kirby, without 

 weighing his authority, has hence concluded that these are 

 the Dactyles of Pliny;** but he should have known that 



* List, de Coch. Exer. Anat. 146. Of Unio pictoram Lister says, " hi 

 autem nmsculi, quibus ova nata sunt ad branchias, hircuni veliemcntcr ole- 

 bant." Exer. Anat. Tert. 18. 



t Land and Freshwater Shells, 56. 



X Linn. Trans, xiv. 160. The Nanina, also a land-mollusk, secretes a 

 green fluid for defence. " The fluid jiourcd out from the oriiiec at the base 

 of the caudal horn-like appendage is of a greenish colour ; it exudes wlien 

 the animal is irritated, and at such times the caudal ajipendage is directed 

 towards the exciting object in such a manner as to give the animal a 

 threatening aspect." — Froc. Zool. Soc. 1834, p. 90. 



§ Syst. Nat. p. 668 ; edit. dec. Oligcrus Jacobaeus, quoted by Owen, 

 asserts that the Cej)halopods are phosphorescent. — Cyclop. Anat. and P/ii/s. 

 i. 526. Mr. C. Darwin noticed that an Octopus which he kept in his cabin, 

 was slightly phosphorescent in the dark. — JoJirnul, iii. 7. 



II " Corpus crassum, latum ; ad partem pallii postcriorem discus margi- 

 natus ex ipso pallio confectus, die viridi lucidus ; nocte phosphorcscens." — 

 Ann.des Sc. i\V//.xxviii. 308; Griffith's Cuvier; xxxix. 328. — Bosc (Coq. 

 iv. 71), and De Montfort (Conchyl. Syst. ii. 216,) assert the lanthina to be 

 phosphorescent, but neither is c;ood authority on this point. 



H Hist. Nat. de Coq. iii. '.).' ** Bridgcw. Treat, i. 240. 



