440 



NATURE 



{March 7, 1889 



to the bottom, or by brushing ofif, on to their coats, eggs 

 which have been already caught by the weeds ; for the 

 ephippial eggs are frequently armed with hooks or spines, 

 which make them adhere easily to a pond-weed or to a 

 hairy coat, and yet would not prevent a dog's vigorous 

 shake, after his bath, from sending them flying into the 

 air, or on to the dust, where sun and wind would do the 

 rest. 



Perhaps one of the most curious illustrations of this 

 aerial conveyance of Rotiferous eggs is the account of 

 Callidina symbiotica, which vi& owe to Dr. Carl Zelinka. 

 It was in the depth of last winter that I read his interest- 

 ing memoir, concerning a new Callidina that he had 

 discovered inhabiting the little green cups on the under 

 surfaces of the leAves of a scale-moss {Friilliana dilatatd). 

 As I knew that this plant grew on the elms of our Clifton 

 promenade, I started off at once, on the rather forlorn 

 hope of finding some living specimens of the new Roti- 

 feron. When I arrived at the promenade I passed patch 

 after patch of the scale-moss, hoping in vain to find 

 something more promising than the withered liver- 

 coloured stuff which alone was ^to be seen on the tree- 

 trunks. At last I gave up further search, and pulling off a 

 scrap of what looked like old ragged carpet, I carried it 

 home. There I put a bit of it into a watch-glass, covered 

 it with water, and gently teased it out with needles, till I 

 found an under frond that had some pretension to being 

 green. This I transferred to a glass cell, and placed it under 

 the microscope with the cups turned towards me ; and it 

 was with no little pleasure that, in about a quarter of an 

 hour, I saw first one Callidina, and then another, stretch 

 its proboscis out of a cup, unfurl its wheels, and begin 

 to feed. 



No wonder that these Philodinadce are to be found 

 everywhere when they can bear to be frozen alive in the 

 cell of a plant, or wasted by a midsummer sun in a leaden 

 gutter ! 



Some chance breeze miist have first wafted a Calli- 

 dina' s t.gg on to the scale-moss, just after a shower, when 

 the whole plant was wet, and thie little green cups were 

 filled with water. The young Callidina, when hatched, 

 could not have desired a better home. The rainfall, on 

 an elm, flows down its furrowed bark in tracks as con- 

 stant as those of a river and its tributaries ; and the growth 

 of \he.Jungermann follows these tracks. Every shower fills 

 the spaces between its flat layers of overlapping leaves 

 with water ; and the lower layers, sheltered by the upper, 

 retain for a long time water enough for the Callidina to 

 creep about or swim in. And when, at last, the sun and 

 air have dried up the water, the creature retreats into its 

 green cup, which presents so small an aperture to the 

 air, and is so fenced round with thick juicy cells, that the 

 contained water is almost certain to hold out till the next 

 shower. If it does not, the Callidina is still content ; it 

 becomes conscious of the coming crisis, draws in its head 

 and foot, rounds its trunk into a ball, secretes round itself 

 a gelatinous covering, and waits for better times. 



But the Rotifera owe their wide dispersion not only to 

 the ease with which their eggs are blown from one place 

 to another, but also to their powers of endurance, and to 

 their marvellous capacity for adapting themselves to new 

 surroundings. A Philodine may say with Howell, " I 

 came tumbling out into the world a true cosmopolite." I 

 have already noticed how the Philodinadce will endure 

 such extremities of heat, cold, and dryness as Nature 

 inflicts on them ; but she does not put their full powers 

 to the test, for, when time is given to them to don their pro- 

 tective coats, they can bear a heat gradually advancing 

 to 200° F., or a fifty days' exposure to a dryness produced 

 over sulphuric acid in the receiver of a good air-pump. 

 Ehrenberg tells us that, whereas he killed Volvox globator 

 with one electric shock, it took two of the same intensity 

 to kill Hydatina senta; and that Rotifer vulgaris will 

 swallow laudanum and yet "be lively," adding that a 



solution of cantharides seemed "to give it new life." 

 The same irrepressible creature will flourish in water 

 containing a perceptible quantity of sulphuric acid, while 

 Asplanchna priodonta will swim about actively for twenty- 

 four hours in a weak solution of salicylic acid, and! 

 Synchceta pectinata will do the same in chromic acid. 

 The great majority of the freshwater species die when 

 dropped into sea-water, but some will bear sudden im- 

 mersion in a mixture of one part sea-water to two fresh. 

 We should not be surprised, therefore, to find not only 

 that there are thirty-four known marine species of Rotifera,, 

 but that seventeen of these species are to be met with 

 alike in salt-water and in fresh. 



The following is the list of Rotifera found in salt or 

 brackish water ; those marked with a star are also the 

 inhabitants of fresh-water : — 



Floscularia campanulata* 

 Melicerta tubicolaria* 

 Rotifer citrinus* 

 Synchseta baltica 



,, tremula (?)* 

 Pleurotrocha leptura (?)* 

 Notommata naias* 

 Proales decipiens* 

 Furcularia forficula* 



,, gracilis* 



,, Reinhardti 



Diglena catellina* 



,, grandis* 

 Distemma raptor 



,, marinum 

 Rattulus calyptus 

 Monostyla quadridentata 



Colurus amblytelus 

 ,, caudatus* 

 ,, dactylotus 

 ,, pedatus 

 ,, uncinatus* 

 Mytilia tavina 

 Pterodina clypeata 

 Brachionus Bakeri* 

 ,, Miilleri 

 Notholca striata* 

 ,, spinifera 

 ,, inermis 

 ,, scapha* 

 ,, thalassia 

 Anuria valga* 

 ,, biremis 

 Hexarthra polyptera. 



Although this is doubtless a very imperfect list, still it 

 is sufficient to show how these fresh-water animals are 

 slowly spreading into the tide-pools on the sea-shore. 

 Some may have commenced their change of habitat in 

 the field drains which are periodically invaded by the 

 brackish waters of a tidal river. It was precisely in such 

 a locality that I first found Brachionus Miilleri, in water 

 only faintly salt, and at a height of 30 feet above the 

 Severn. Ditches of this kind are to be found all down 

 the Avon ; from the highest point, that the tide reaches,^ 

 to its mouth. As they approach the Severn their water 

 becomes more and more brackish, and the preponder- 

 ance of marine species in them more pronounced ; so that 

 it is easy to see how the descendants of a fresh-water 

 Rotiferon, passing slowly down the river-side from ditch 

 to ditch, may in course of many generations come to 

 endure the sea itself. 



In other cases the air-borne eggs may have dropped 

 into the pools, of every degree of brackishness, which 

 usually skirt the shores of our river estuaries. It is in 

 such places, on the Scottish shore, that Mr. John Hood 

 has found so many new marine species, and where no 

 doubt so many more are yet to be found. 



But the most noteworthy point about the above list is 

 that the number of distinct genera is so great. One 

 would rather have expected to find but four or five 

 genera hardy enough to endure salt water ; and yet here 

 are no fewer than nineteen genera for the thirty-four 

 known marine species ; and of these latter, seventeen spe- 

 cies are yet in the transitional state, inhabiting alike salt 

 waters and fresh. Still more curious is it to find that all' 

 the four orders are represented ; and that Rhizota, Bdel- 

 loida, and Scirtopoda have each furnished a contingent 

 to the marine forms, as well as the more frequent Ploima. 

 It is, of course, rather startling to hear that Melicerta and 

 Floscularia are to be found inhabiting sea-water ; but I 

 know of no reason why any doubt should be thrown on 

 Dr. Weisse's record of having so found them on the sea- 

 shore at Hapsal. 



The capacity of the Rotifera for adapting themselves to 

 new surroundings is shown by a mere enumeration of the 



