December 7, 1893] 



NA TURE 



127 



adjacent to it. Also, with such arrangements below as 

 those of the Victoria, it is impossible to ensure that an 

 unforeseen accident would always allow of sufficient time 

 to close the water-tight doors in the manner required. 



The efficiency of the water-tight hatches, and the 

 chances of their being properly secured in an emergency 

 when they are fastened by a number of clips round the 

 ■edge, as at present, is also a question that appears to re- 

 quire consideration ; while it is to be observed that the 

 sliding horizontal door in the protective deck of the 

 Victoria, which opened into a shoot through which coal 

 was trimmed from the reserve bunkers at after end of 

 protective deck, into the side bunkers in the stokehold, 

 could not be closed from the shoot in which the men 

 worked who were trimming the coal ; but had to be 

 worked from the submerged torpedo room, a compart- 

 ment below the protective deck. This open door had an 

 important effect upon the capsizing, for Mr. White states 

 that "one of the chief causes of inclination to starboard 

 is to be found in the fact that, owing to open doors, water 

 was able to find its way from bunkers above the protec- 

 tive deck, down through the coal-shoot, and so to fill 

 No. 7 bunker just before the forward starboard stoke- 

 hold.^' 



It appears to us that one of the chief lessons taught by 

 the circumstances of this disaster, is the necessity of 

 reducing the number of water-tight doors and hatches, and 

 of arranging that all of them which are essential to the 

 efficiency of the water-tight subdivision, and are ever 

 likely to be left without attendance while open, should be 

 capable of being closed, either by a thoroughly satisfac- 

 tory self-acting arrangement, or by appliances for work- 

 ing them from a deck at a safe height above water. 



The points still remaining to be considered will be 

 reserved for cur next article. 



Francis Elgar. 



REAPPEARANCE OF THE FRESHWATER 

 MEDUSA {LIMNOCODIUM SO IVERBH). 



FOR three years nothing has been seen of the fresh- 

 water medusa in the Regent's Park, and naturalists 

 liad given up hope of carrying on any further investiga- 

 tion into its life-history. It seemed as though this beauti- 

 ful little organism -brought we know not how or whence 

 into the midst of London — had, like some mysterious 

 ■comet, unexpectedly burst on the zoological world, and 

 as unexpectedly disappeared. 



I was, therefore, greatly astonished to hear in September, 

 from my friend the Director of Kew, that the curator of the 

 Sheffield Botanic Gardens (Mr. Harrow) had discovered 

 it in quantity in the Victoria Regia tank under his care 

 during the present summer, and I was soon after delighted 

 by the safe arrival from Sheffield of a bottle containing 

 living well-grown specimens of the familiar jelly-fish. Mr. 

 Harrov/ informs me that he observed it in the tank at 

 Sheffield for the first time in the beginning of June of 

 this year (1893). Specimens were still observed as late 

 as the middle of October — giving a duration of some 

 fourteen weeks— an unusually long period. Mr. Harrow 

 estimates the total number seen as at least 300. 



The last seen in the Botanic Gardens, Regent's Park, 

 London, were taken from the new Victoria Regia tank 

 on July 30, 1 890. The question as to how the jelly-fish got 

 to Sheffield is easily answered. Water plants (Nymphae- 

 aceee and Pontederia) were sent (as I am informed 

 by Mr. Sowerby and by Mr. Harrow) from Regent's Park 

 to Sheffield to re-stock the tank there on April 4, 1892, 

 and on April 7, 1893. Hence there was the probability 

 of some of whatever reproductive germs of Limnocodium 

 existed in Regent's Park being transferred to Sheffield. 

 The curious thing is that in 1892 and in i8gi no Limno- 

 codium were seen in the original source — viz. the Regent's 



NO. 1258, VOL. 49] 



Park tank — nor in 1893, excepting a few sent from Shef- 

 field and placed in that tank by Mr. Sowerby. 



This is the first instance recorded in which another 

 Victoria Regia tank has been "infected" with Limno- 

 codium from the original Regent's Park tank, excepting 

 when the new tank in Regent's Park was in 1890 infected 

 from the old one — by the transference to it of weeds and 

 roots containing the germs of the jelly-fish. 



The tank at Kew has never been properly infected, for 

 it is, I regret to say, the anti-zoological custom at the 

 Royal Gardens to thoroughly cleanse, wash, and furbish 

 up the Victoria Regia tank every year so thoroughly that 

 the winter germs of the jelly-fish are removed or destroyed. 

 Hence Limnocodium has flourished at Kew when sent 

 there from Regent's Park, but has never " carried over " 

 from one season to another. It is, fortunately, the 

 custom in other botanical gardens to leave a quantity of 

 " sludge " (including some old leaves and stems) at the 

 bottom of the tank, when the water is drawn off and 

 the soil prepared for a new season, and hence Limno- 

 codium has been preserved from destruction for so many 

 years. 



As to what is the precise nature of the process by 

 which Limnocodium has been carried over from one 

 season to another in the Regent's Park, we are still uncer- 

 tain. The facts at first ascertained were these, viz. that 

 the jelly-fish suddenly appear each year as early as April 

 or as late as August, and remain for from five to twelve 

 weeks, when they die down and absolutely disappear. 

 During the first few weeks of their appearance the water 

 is found to contain an immense number of minute young 

 forms (jj\, of an inch in diameter), which I described 

 and figured in the Quart. Joiirn. Micros. Science, vol. 

 xxi. p. 194. Evidently these young were being pro- 

 duced in quantity in the tank, and gradually developed to 

 the full size of half an inch diameter. The form and 

 appearance of these young were such as to lead me to the 

 conclusion (subsequently found to be eri'oneous) that they 

 had been developed from eggs. At the same time the 

 remarkable fact was established by the examination in 

 successive years of many hundred specimens that the 

 adult Linuiocodia were every one, without exception, 

 males. They produced abundant motile spermatozoa, 

 but not a trace of an egg-cell was ever found in any one 

 of them ! 



The hypothesis which I entertained in 1884 as an 

 explanation of this curious state of things was — that the 

 female was a non-motile, perhaps a fixed hydriform 

 organism, and I accordingly searched for such a form in 

 the mud and debris from the bottom of the tank. At 

 last, in a large quantity of such material which I 

 obtained when the tank was cleared out in the winter of 

 1884, my assistant, Dr. A. G. Bourne, found a very strange 

 diminutive polyp adhering in numbers to the root- 

 filaments of Pontederia. This polyp he carefully de- 

 scribed in the same year in a communication to the Royal 

 Society. There was very great probability that this little 

 polyp, devoid of tentacles, and not more than |th of an 

 inch long, was the " trophosome " of the Limnocodium 

 medusa. That this was a true inference was subse- 

 quently proved by Dr. G. H. Fowler, who in 1890 {Quart. 

 Journ. Alicros. Science, vol. xxx.) the last year in which 

 the jelly-fish were seen in London, showed that the little 

 spherical young found floating in the water of the tank 

 are nipped oft" by a process of transverse fixion from the 

 free ends of the minute polyps described by Bourne. 



Fowler (whose observations were made in my labora- 

 tory in 1888) found the polyps very abundantly upon 

 floating water-plants widely scattered in the tank ; they 

 were also detected by Mr. Parsons, of the Ouecket Club, 

 in water which was the overflow of the tank, and accumu- 

 lated in an outside reservoir. 



The immediate question then became " How do the 

 polyps originate ? " The polyps account for the medusse, 



