ADAMS : OBSERVATIONS ON THE PAIRING OF UMAX MAXIMUS L. 93 



at the finish. On one occasion, however, the fall was very gradual, 

 and during the descent the couple were busily eating more mucus 

 from each other's bodies. The thread appears to come from their 

 mouths, and runs along the centre of the footsole of each, joining 

 into a single thread where their tails intertwine. The upper part of 

 the thread is joined to the circular patch of mucus left on the wall 

 where their previous gyrations have taken place. I have seen a 

 couple suspended in space from a projecting beam in an outhouse, 

 and also from the leaves of a currant bush, and also from the branch 

 of a yew tree, and once from a glass pane of a greenhouse ; but a 

 perpendicular wall or tree-trunk is the usual situation. 



Directly the descent is accomplished, an organ is protruded from 

 the genital orifice of each. This organ, cylindrical at first, quickly 

 assumes a club-shape of from i| — if inches in length (PI. III., fig. i), 

 but presently a frilled edge appears along one side (fig. 2) as if un- 

 rolled, and in a second or two the unrolling is complete, and the 

 organs assume the shape of fig. 3. The organ along the inner curve of 

 the figure is thick and rounded, while the edge of ths whole outer curve 

 is thin and sharp. The unrolled organs now commence to intertwine 

 (fig. 4), finally closing round each other so as to form a knot (fig. 5), 

 of which it is easy to count the whorls. The two upper whorls of the 

 knot thus formed now spread out in the form of a mushroom or 

 umbrella, leaving the lower portion of the knot as before (fig. 9). 

 Fig. 7 gives the view of this from above. Sometimes the two out- 

 spread whorls do not overlap as in fig. 9, but curve in different 

 directions as shown in fig. 8, and sometimes they are nearly horizontal, 

 but separate as in fig. 6. The colour of the extruded organs is milk 

 white, flecked here and there with dead white. During 5 — 10 minutes 

 the slugs hang motionless with the tentacles contracted and flabby, 

 while the two upper outspread whorls keep revolving upon one another ; 

 and in this extraordinary manner the mutual act is consummated. 

 This ended, the process above described is reversed ; the organs un- 

 wind, roll up and finally disappear. 



It now usually happens that one slug drops to the ground and lies 

 there for sometimes 15 minutes motionless and apparently exhausted, 

 and finally crawls away ; while the other doubles down its head and 

 picks up the supporting thread in its mouth from the centre of its own 

 footsole and climbs up to the point of support, eating the thread as it 

 goes. Frequently the animal will then descend the thread (which 

 usually adheres to the wall) and eat more of it, and on one occasion I 

 saw an individual ascend the thread again and consume all that was 

 left. It often happens that the thread is left untouched and it may be 

 seen for days on the side of a wall or tree trunk. On the occasions 

 when the pair were suspended from the projecting beam neither of 



