March 7, i 



NA rURE 



439 



minute creatures, who are inhabitants of lakes, ponds, 

 ditches, 'and sea-shore pools, contrive to spread them- 

 selves so widely ov"fer the earth ? Take, for instance, the 

 case of Ayplanchmi ebbesbornii, which till quite lately had 

 but one known habitat, viz. a small duck-pond in a 

 vicarage garden in Wiltshire. The very same animal 

 has been found by Mr. Whitelegge in the botanical gardens 

 at Sydney, New South Wales. No doubt, in time, it will 

 be found elsewhere also ; but how, or when, did it pass 

 from the one spot to the other? 



Again, there is the strange Floscule, F. Millsii, a 

 Rotiferon apparently linking together the genera 

 Flosciilaria and Stephanoccros, and which has been 

 found almost simultaneously by Mr. Whitelegge at 

 Sydney, and Dr. Kellicott at Ontario. The possibility 

 of its journeying between two such points seems quite 

 as hopeless as that oi Ashplanchna cbbcsborniVs passing 

 from New South Wales to Wiltshire. 



And such cases are numerous. How did Hydatina 

 senta and Bnichionics pala ge?t to New Zealand? or 

 Notops bracliicmus and Rotifer vulgaris to the top of 

 Adam's Peak, and the Pampas of La Plata ? Again, there 

 is Pedalion minim : since I first found it, in a pond at 

 the top of Nightingale Valley, at Clifton, it has been met 

 with in four or five other places in England, including a 

 warm water-lily tank at Eaton Hall ; but, till quite 

 lately, in no other country. Now I have just received a! 

 letter from Mr. Gunson Thorpe, telling me that he has 

 found it swarming in a pool on a rocky headland in 

 Queensland. 



You have, n.o doubt, long ere this anticipated the solu- 

 tion of the puzzle, and see clearly enough that living 

 creatures, to whom a yard of sea- water is as impassable a 

 barrier as a thousand miles of ocean, could only have 

 reached or left Australia, New Zealand, Jamaica, Ceylon, 

 •&C., in the egg ; not the soft, delicately shelled, and quickly 

 hatching summer &<g%, but the ephippial ^gg, which is 

 protected by a much harder and thicker covering, which 

 is constructed so as to bear without injury a long absence 

 from the water, and which hatches, so far as is known, 

 some months after it has been laid. 



But this explanation still requires to be explained. The 

 case of the free-swimming Rotifera is simple enough. 

 They are most of them to be found, at some time or 

 another, in small shallow pools, and their eggs either 

 fall to the bottom of the water, or are attached to the 

 small confervoid growth on the stones in it. Such pools 

 frequently dry up, leaving the ephippial eggs to wait for 

 the rainy warm weather of next year. Then comes 

 boisterous weather, and the dusty surface of the exposed 

 bottom of the pool is swept by a wind, which raises the 

 dust high into the air, ephippial eggs and all. For these 

 latter are minute things ; few exceeding one three-hun- 

 dredth of an inch in length, and many even half that 

 size. Once raised in the air, I see no reason why they 

 should not be driven by aerial currents, unharmed, half 

 round the globe, falling occasionally in places where 

 water, temperature, and food are alike suitable. 



The dust of the eruption at Krakatao, which gave us 

 such wonderful sunsets and green moons in 1883, 

 travelled from the Sunda Isles to England in three 

 months ; and so the ephippial eggs of AspUinchna 

 ebbesbornii, and other Rotifera, may have traversed the 

 distance from England to Australia, and yet have been 

 capable of hatching at the end of the journey. 



It may perhaps seem a fanciful notion to account, for 

 the stocking of the ponds at Sydney by eggs carried 

 thousands of miles in the air, but several well-known 

 facts warrant the hypothesis. The tops of our houses, 

 the heights of the Alps, the slopes of the Siberian moun- 

 tain ranges, are haunts of the Philodines, which, being an 

 exceptionally hardy race, have accommodated themselves 

 to living in damp mosses at the edge of a glacier, or in a 

 gutter which now holds a mere handful of stagnant water, 



now is a racing current, and now a dusty leaden basin, 

 glowing under a blazing sun. No doubt eggs of all sorts 

 of species fall on the same spots, but only to perish 

 under trials that none but a Philodine could survive. 



How various are the species whose eggs are thus 

 wafted up by the air has been well shown by Mr. J. E. 

 Lord, who has given a list of no fewer than forty-five 

 species (cpntained in twenty-nine genera) that he found, 

 in the course of twelve months, in the same garden pond. 

 It was, however, admirably situated for catching whatever 

 there was to be caught, for it lay in a flat plot of ground, 

 where there was an. entire absence of trees and shade, 

 so that its surface was fully exposed to every wind that 

 blew. 



The eggs, of course, must often fall on unsuitable places, 

 and be carried past suitable ones, and this accounts for 

 the capricious appearances of Rotifera in some well- 

 watched ponds, and for the frequent disappointments of 

 the naturalists who visit it. To this aerial carriage of 

 the eggs is also due the otherwise perplexing fact that, 

 when any rare Rotiferon is found in one spot, it is fre- 

 quently found at the same time in closely neighbouring 

 ponds and ditches, even in such an unlikely hole as the 

 print of a cow's foot filled with rain, but not at all in more 

 promising places at some distance off. 



Admitting, then, this fitful shower of eggs as proven, we 

 at once see another way in which they may readily travel 

 to. distant lands. For it is quite possible that now and 

 then they may fall on the cargo of an outgoing ship. 

 Here they might lie safely in cracks and creases till, the 

 journey being over, the knocking apart of packing-cases 

 and the shaking of wrappers would set them atloat again, 

 to drop down, it may be, into the Botanical Gardens of 

 Sydney, the shore-pools of Ceylon, or the ponds of 

 Jamaica. In fact, these Rotifera would have really done 

 what I have already pointed out that they seemed to do — 

 they would have followed the flag. 



The eggs of the tube-makers, however, and of such 

 Rotifera as live only in the clear waters of lakes and deep 

 ponds, present a greater difficulty, for their eggs either lie 

 within their tubes, or are attached to growing weeds, or 

 fall down to a bottom which lies covered all the year 

 round with several feet of water. The wind and sun 

 here cannot be the only means of dispersion. Aquatic 

 birds, and dogs, are probably assisting agents. The birds, 

 as they swim among the water-plants, must frequently 

 set free the eggs from the tubes of the Rhizota, as well as 

 those which adhere to ConfervK, Potomagetons,and water- 

 lilies, and so get them attached to their feathers. Then 

 away they fly, carrying the eggs to some far distant lake, 

 or shaking them off into the air with the flapping of 

 their wings. 



In confirmation of this idea, I may mention that the 

 well-known naturalist, Mr. John Hood, of Dundee, who 

 has added so many remarkable species of Rhizota to our 

 Rotiferous fauna, informs me that the Scotch lakes most 

 prolific in new and rare species are those which are 

 visited annually by wild fowl from the North. Prof. 

 Leidy also informs me that his collector, Mr. Seal, 

 noticed sand-pipers haunting the duck-pond where he 

 found an Asplanchna very similar to vbbesbcrnii, and 

 that he thought that "these birds were especially instru- 

 mental in distributing the lower forms of aquatic life." I 

 miy also add that on one occasion I found in a temporary 

 rain puddle, barely a yard across, a living ciliated ovum 

 of Flumatclla rcpens. Of course the puddle itself con- 

 tained no adult forms, and the ovum must have been 

 brought by some bird the distance of at least half a mile. 

 The twin polypes were already partially developed inside 

 the ovum^iand it is curious that so delicate a thing should 

 have borne this transport safely. 



Dogs probably play a humbler part in the dispersion of 

 the Rotifera ; but they cannot help taking some part in it,, 

 by intercepting, as they swim, eggs that are slowly sinking 



