Nov. 12, 1874J 



NA TURE 



Locomotion of Medusidse 



I DO not think that the following remarkable observation has 

 hitherto been made — or at least recorded — by anyone ; but as I 

 am at present deprived of access to books, il is possible that I 

 may be mistaken upon this point. It will be observed that it tends 

 experimentally to confirm the opinion of Agassiz, M'Crady, and 

 Fritz M tiller, as to the presence of ganglionic centres in the 

 situations they describe. 



Slabbcria conua is, as its specific name implies, a medusid of a 

 conical form, and its size is about that of a fully-developed acorn. 

 Itspolypite, which is of unusual proportional length, is highly con- 

 tractile ; and its swimming-bell (lurtoca/yx) supports four short 

 slender tentacles, which are likewise highly contractile. These 

 tentacles take their respective origins from four minute vesicular- 

 like bodies (marginal •resides), wliich are so situated in the margin 

 of the nectocalyx as to mark off this circular margin into four exact 

 quadrants. If any one of these vesicular-like bodies be excised, 

 immediate and total paralysis ensues in the segment of the cone 

 in which it is situated ; i.c:, a fourth part of the entire animal 

 ceases to contract. If two adjacent vesicles are excised, one half 

 of the entire animal becomes paralysed, the loss of motion 

 being quite as decided, and the area of its occurrence quite as 

 well defined, as in the case of hemi-section of the spinal cord. 

 If two opposite vesicles are removed, cross paralysis results ; if 

 three of these bodies are cut out, only one quarter of the cone 

 continues to contract ; and lastly, if they are all taken away, 

 every vestige of contractility immediately disappears, not only in 

 the nectocalyx, but also in the polypite. Now, as the bodies in 

 question are not so large as are the dots over the letter " i " in this 

 printed description, the extreme localisation of stimulating in- 

 fluence thus shown to exist cannot but be deemed a highly 

 remarkable fact, more especially as no amount of mechanical or 

 chemical irritation will cause the slightest contraction in any part 

 of the animal subsequent to the removal of these four almost 

 microscopical points ; while, contrariwise, so long as any portion 

 of tissue (no matter how small) is left united to one of these 

 points, it wUl continue its rhythmical movements for an indefinite 

 period of time. Thus, for example, when a section is made 

 through the equator of tlie animal, while the upper half at once 

 ceases to move, the lower half — now converted into an open 

 ring — continues its contractile motions for days with unimpaired 

 energy, notwithstanding the thus mutilated organism is, of 

 course, unable to progress. 



It is well known that when the entire margin of the necto- 

 calyx of a medusid is removed, the contractility of the remaining 

 portion is destroyed. This fact is usually explained by supposing 

 that t)ie severance of all the contractile fibres produces what may 

 be called mechanical paralysis, just as a man could not move his 

 arm if all its muscles were divided. Experiments I have made 

 on other species o{ Mediisidit have led me to doubt the truth of 

 this explanation — at all events as the whole explanation ; but it 

 is unnecessary to detail these at present. The instance above 

 given is enough to show that in the case of this species, at any 

 rate, such an explanation is clearly insufficient, and my object in 

 now writing is to request that if any of your readers are acquainted 

 with observations (whether published or not) similar to those 

 described, they should kindly let me know, either through your 

 columns, or by writing to Gonville and Caius College, 

 Cambridge. GEORGE J. ROMANES 



Dunskaith, Ross-shire 



Suicide of a Scorpion 



I SHALL feel obliged if you will record in N.A.TURE a fact with 

 reference to tlie common Black .Scorpion of Southern India, 

 which was observed by me some years ago in Madras. 



One morning a servant brought to me a very 'arge specimen 

 of this scorpion, which, having stayed out too long in its nocturnal 

 rambles, had apparently got bewUdered at daybreak, and been 

 unable to find its way home. To keep it siife, the creature was 

 at once put into a glazed entomological case. Having a few 

 leisure minutes in the course of the forenoon, I thought I would 

 see how my prisoner was getting on, and to have a better view 

 of it the case was placed in a window, in the rays of a hot sun. 

 The li^t and heat seemed to irritate it very much, and this 

 recalled to my mind a story which I had read somewhere, that a 

 scorpion, on being surrounded with fire, had committed suicide. 

 I hesitated about subjecimg my pet to such a terrible ordeal, but 

 taking a common botanical lens, I focused the rays of the sun on 

 its back. The moment this was done it began to run hurriedly 



about the case, hissing and spitting in a very fierce way. This 

 experiment was repeated some four or five times with like results 

 but on trying it once again, the scorpion turned up its tail and 

 plunged the sting, quick as lighming, into its own back. The 

 nitliction of the wound was followed by a sudden escape of fluid, 

 and a friend standing by me called out, " See, it has stung itself; 

 it is dead ; " and sure enough in less than half a minute life was 

 quite extinct. I have written this brief notice to show (i) That 

 anim.als may commit suicide ; (2) That the poison of certain 

 animals may be destructive to themselves. 



Bridge of Allan, N.D., Oct. 23 G. BiDIE 



THE AMU EXPEDITION 



"\X7'E give some extracts from a letter relating to the 



* "' hydraulics of the Amii, sent us by an English 

 engineer who was with the expedition ; the letter is dated 

 " Nukus, at the head of Amii delta, Sept. 10, 1874 : " — 



The expedition only arrived in the delta at the 

 end of June ; it is impossible, therefore, to say at what 

 date the first spring flood of the river takes place, 

 but probably between the ist and 15th of May. The 

 level of the river on June 23 was what may be called a 

 low-level full river : it fell about twelve centitnetres till 

 June 29, and then rose rapidly till July 11, when it was 145 

 centimetres above the level of Juno 23. It then fell fifty 

 centimetres up to July 17, and rose again to nearly the 

 previous height on Aug. 4. Since that date the river has 

 fallen steadily, and is to-day some fifty centimetres below 

 thelevelof June 23. I judge the heights of July iiandAug. 

 4 to be the extreme flood level of the Amii. At that flood 

 level, the discharge at Toyu-boyin, " The Camel's Neck," 

 160 miles above the head of the delta, cannot be far short 

 of 140,000 cubic feet per second. It is difficult to say 

 what the low-water discharge is, but I should think it is 

 at least 70,000 cubic feet per second.* On Aug. 25, by a 

 rough observation, it was 110,000 cubic feet a second, the 

 river then being 25 centimetres above the level of June 

 23. At Toyu-boyin the river has cut its way through a 

 bed of shelly limestone of the age of the chalk. The 

 limestone is very compact and hard, full of small shells, 

 turritella and bivalves. Here the river is 1,000 ft. broad. 

 The height to which the limestone bed has been tilted 

 is about 25 ft. The river expands in breath immediately 

 afterwards to 2,000 ft. or more, for about five miles ; it 

 then begins to contract again, having on its left a high 

 bank of hard clay passing almost into an argillaceous 

 schist. This high bank extends for above five miles, and 

 ends in an eminence of 50 or 60 ft. in height, crowned 

 with sand. From Toyu-boyin downwards on the right 

 bank, are ridges (of clay, I imagine) crowned with sand : 

 no cultivation on that bank, but opposite and downwards 

 from Toyu-boyin irrigation canals are taken off, excepting 

 where the high clay bank occurs. At the eminence 

 spoken of the river immediately widens to 5,000 ft. or so ; 

 this is caused by the first large irrigation canal Polwan. 

 As these canals have a great effect on the river all the 

 way down to the delta, 1 will here try and explain my theory 

 on the subject. As the Amu runs in a soft soil from the 

 south to north nearly in the direction of the meridian, 

 I imagine what the Russians call the law of Bar (from 

 his observations on the Volga) comes into action. The 

 stream has therefore the tendency to run along the right 

 bank, and, as a matter of fact, the deep-water channel is 

 there found. If, then, an irrigation canal be opened on 

 the left bank, the stream is disturbed and a subsidiary 

 deep channel is formed towards the head of the canal 

 (Fig. I.) The head of the canal is only open during 

 flood, say half the year. When it is shut, the river will 

 run as in Fig. 2 : silt will be found at the shaded 

 parts. The river by Bar's law will edge away to the right 

 and become broader, and if this process is continued 



* Perhaps this is too high — I cannot make out from Wood's " Cxiis " more 

 than 45,000 cubic feet or so per second lor winter discharge. 



