Mollnsca. 



6273 



has acquired a sufficient consistence, they hegin to twist around each other, and detach 

 themselves from the wall,"^ hanging only by a cord formed of the thickened mucus ; 

 as they hang suspended, they still keep twisting themselves around each other, 

 forming a double spiral ; they continue this turning motion ten minutes or more, until 

 at last their bodies can hardly be distinguished from each other, thus forming a regular 

 cone about two inches in length and the base one or two inches in diameter, hanging 

 from its apex ; during this time the mucous cord keeps lengthening slowly (in one 

 instance it reached about fifteen inches in length ; I have not seen any less than eight 

 or nine inches) ; the organs of generation are then protruded from their orifice near 

 the mouth, and, hanging down a short distance, touch each other; they then commence 

 the same spiral motion, twisting round each other, resembling a two-stranded cord. 

 When fully protruded they cannot be distinguished ; the lower part then assumes 

 various forms : the first I saw resembled an inverted flat-topped agaric, the portion 

 forming the stem being about two inches in length and two or three lines in diameter, 

 the top being about an inch and a half across : others have formed an ovoid mass 

 suspended in like manner, covered with foliated processes similar to those of a foliated 

 Murex or a leaf of curled parsley ; at this time they form a very beautiful object, 

 especially when they hang from some projecting surface, which enables them to swing 

 clear without touching the wall ; the dark shell-like substance hanging pendant from 

 a white shining cord, one line in thickness, below which hangs another white semi- 

 transparent body, the delicately striated surface of which shows all over it; a 

 continuous vermicular motion ; the foliated expansions, continually changing their 

 form or being withdrawn in places and shooting out afresh in others, giving out occa- 

 sionally an iridescence, as the light falls upon the ever-varying surface. After 

 remaining a considerable time in this position (the vermicular motion continuing 

 without intermission) the generative organs separate, and when nearly withdrawn, the 

 bodies untwist themselves and separate ; they then crawl up the suspending line and 

 depart. I suppose the reason why they have not been previously observed is, that it 

 always takes place late at night : I have never observed them before eleven o'clock, 

 but generally about midnight. If persons observe, where the slugs abound, circular 

 patches of slime on the walls, formed during the previous nights (being so much more 

 in thickness than the shining tracks they make, they are not obliterated for two or three 

 days), they may be sure that by attentively observing them the next sultry nights, they 

 will most probably be able to verify the foregoing statement of facts. Bladon ; 

 Pont-y-pool, September 30, 1858. 



* I have not been able to observe the actual separation from the wall, my 

 attention being unfortunately called off for a minute or two from them ; in the case in 

 which I had an opportunity of tracing the whole process from commencement to end, 

 I left them when they were forming the circular patch of mucus, and when I 

 returned they had just left the wall and were commencing the secretion of the 

 suspending cord. 



XVI. 



3h 



