290 



NA TURE 



\Augtist 9, 1877 



psss the barrieis are only very feeble, the next stronger, 

 the next still stronger, and so on, according as the new 

 passage becomes niore and more permeable by use; until 

 at last the contractile w.ives pour over the original barrier 

 without any perceptible diminution of their force. In 

 some cases, by exploring with graduated stimuli and 

 needle-point teiminals, I was able to ascertain the precise 

 line through which this erupjtion of stimulating influence 

 hnd taken place ; so that altogether I think these facts 

 tend ver) strongly to confirm Mr. Spencei's theory regard- 



ing the genesis of nerves.' I will only add that if this 

 interpretation of the facts is correct, we have in them a 

 striking instance of the uniformity with which Nature 

 works. A scientific theory concerning the evolution of 

 nerves, which a year or two ago it seemed impossible to 



i forward 'fl'ith a strength sulTicient 

 in the polypiie. I may here adr) that thin: fact of the contractile waves being 

 sometimes wholly blocked by section before the stimulus waves are so, would 

 appear to exclude, in the case of the Medusae at all events, Kleir.eiiberg's 

 view as to the functions of primitive nerve and muscle being b ended in the 

 same tissue-elements. (See his work on //j'^r^r ) I may also mention that 

 in some cases I have obseived that the establishing of a new line of physio- 

 logical connection is a more graduril process than stated in the text. To show 

 this. I may briefly quote one very instructive case. Seven marginal bodies 

 having been removed, 'he eighth one continued to originate contractile waves, 

 which coursed roimd the swimming-bell as us al. 1 no'v made a radial cut 

 halt" an inch on one side of the marginal body, and extending to the centre of 

 the swimming-bell. The contractile waves were immediate ly blocked - thus 

 showing, as did a somewhat similar experiment detailed in my first Royal So- 

 ciety paper (p. 293), "' that the influence of the marginal body had previously 

 been communicated to the swimming-bell from oite side only:^ But in the case 

 we are now considering, the discharges of the marginal body were still rendered 

 aoparent by very local contractions of a tissue area in the immediate vicinity 

 of that body — the area, namely, which in the figure (Fig. 6) representing one 

 end of the strip is marked B B. Exploration by stimulus now showed that 

 gener.nl contractile waves could only be started outside the area B B. In some- 

 what more than half an hour after ihe operation (during which time the area 

 E B continued to contract rhythmically), the ganglionic influence for the first 

 time extended from the area B B to the rest of the strip— the contraction being 

 therefore general. After this first eruption of contractile influence, there 

 succeeded a period of about a minute, during which the area B B continued 

 to contract independently as before. Then another eruption took place, fol- 

 lowed by another period of restricted contraction, and soon. Next, these gene- 

 ral con.ractions became progressively more and more frequent, and as the 

 rhythm always continued the same, whether the contraclions were local or 

 general, the number of the latter became ircreased at the expense of that of 

 the former. Tnus, while at first there were twenty or thirty local contrac- 

 tions between every two general contractions, this proportion gradually fell 

 to fifteen, ten, five, &c , till the nun.bers became equal, after which Ihe 

 balance began to incline in favour of the general contractions Eventually 

 the local contractions ceased altogether, and on now excising the marginal 

 body and exploring by stimulus, I was able to localise very precisely the 

 line through which physiological continuity had been C'tablished between 

 B B and the rest of the conlrattile strip. This hne was AC, as shown by the 

 fact that while stimulation of any other pan of the area B B was followed only 

 by a local contraction at that area, stimulation of the line A c was alwajs 

 tuUowtd by a general contraction. — G. J. K. 



verify, from the fact that it seemed as though the ob- 

 servations which would be required to verify it would 

 need to ex'end over thousands of years — this theory is 

 now, I believe, being verified by observations which need 

 only extend over hours and minutes. The immensely 

 protracted history of nervo-genesis upon this planet is 

 thus probably reproduced in a greatly foreshortened 

 manner in the facts which I have explained ; and in- 

 conceivable as is the difterence between these two his- 

 tories of nervo-genesis in respect of their duration, it is 

 nevertheless most probably in respect of 

 their duration alone that these two his- 

 tories differ. 



I will now invite your attention to 

 another species of Medusa, which is of a 

 somewhat mere highly evolved type than 

 A/ireh'a,3nd which I have called Tiaropsis 

 nidicans \^\'g.'j),\n allusion to a highly 

 7/ interesting and impoitant function which 

 / is displayed by its pulypite. This function 

 consists in that organ localising, v/ith the 

 utmost precision, any point of stimulation 

 situated in the bell. For instance, if the 

 bell be pricked with a needle at this 

 point (a), the polypite immediately moves 

 over and touches that point, as repre- 

 sented in the diagram. If immediately 

 afterwards any other part of the bell be 

 pricked, the polypile moves over to that 

 part, and so on. Now this, you will per- 

 ceive, is a highly remr.rkable function ; for it proves 

 that all parts of the bell must be pervaded by lines 

 of discharge, every one of which is capable of conveying 

 a separate stimulus to the polypite, and so of en- 

 abling the polypite always to determine which of the 

 whole multitude is being stimulated. This localising 

 function of the polypite, therefore, shows that the lines of 

 discharge must be more differentiated in this species than 

 they are in Aurciia ; for it shows that vicarious action 

 cannot be possible among them in so high a degree : 

 every line of discharge must here have acquired a more 

 specialised character, in order that the message which it 

 conveys to the polypite when itself directly stimulated 



may not be confused with that which is conveyed by any 

 other line. 



Now It is easy to be wise after the event ; but the state 

 of things we here observe is just such a state of things as 

 I think we should expect to constitute the next stage of 

 nervo-evolution. It is no doubt a benefit to this Medusa 

 that its polypite is able to localise a seat of stimulation in 

 the bell ; for the end of the polypite is provided with a 

 stinging apparatus, and is besides the mouth of the 

 animal. Consequently, when any living object touches 

 the bell — whether it be an enemy or a creature serving as 

 prey — it must alike be an advantage to the Medusa that 

 its polypite is able to move over quickly to the right spot, 



