252 Royal Society : — 



sent in the swimming-organs of Medusno. I Lave hitherto failed, 

 however, to detect any snch lines histologically. 



(h) After the waves have become completely blocked in a con- 

 tractile strip, it sometimes happens that the blocking is overcome, 

 the waves again passing into the remainder of the gonocalyx as 

 freely as they did before the section reached the point at which 

 the blocking occurred. Sometimes, under these circumstances, 

 the strip will admit of being further elongated for some distance 

 before the waves are agam blocked ; and occasionally it happens 

 that the second blockage is also thrown down. I have once 

 seen four such successive blockages successively overcome. 



It will be seen that these facts militate against the supposition 

 of Hues of discharge being present. I think, however, that there 

 is a theory by which these facts admit of being satisfactorily recon- 

 ciled with that supposition. But this whole subject awaits fur- 

 ther and extensive investigation. 



(c) Pressure exerted upon any transverse line in a contractile 

 strip causes blocking of the waves at that hne. If the pressure be 

 slight, the blocking will be temporary ; but if severe or long-con- 

 tinued, the blocking will probably be permanent. Even the slight 

 strains caused by handling contractile strips in the air are often 

 sufficient to show the rate of the waves, and sometimes to block 

 them. 



y. Additional Facts tending to sliniu the identity of tlie Locomotor 

 Centres of Medusai u'ith Nervous Tissue in genercd. 



§ 1. Having placed several hundred Sarsi(e in a large bell-jar, I 

 completely shut out the daylight from the room in which the jar 

 was placed. By means of a dark-lantern and a concentrating-lens, 

 I then cast a beam of light through the water in which the Sarsire 

 were swimming. From all parts of the bell-jar the Sarsice crowded 

 into the path of the beam. The presence of a visual sense in 

 the case of this genus is therefore unquestionable. 



Having removed twelve vigorous specimens from the large bell- 

 jar and placed them in a smaller one, I excised the so-called eye- 

 specks from nine of the number. The three unmutilated indivi- 

 duals sought the light as before ; but the other nine swam hither 

 and thither without paying it any regard. I conclude, therefore, 

 that the visual faculty is lodged exclusively in the marginal bodies. 



Lastly, I brought a heated iron, just ceasing to be red, close 

 against "the glass side of the large bell-jar ; but no one of its nume- 

 rous occupants approached the heated metal. Therefore the rays by 

 which the Sarsia; had been affected in the previous experiment wei'e 

 the properly luminous rays, and not the calorific ones. 



§ 2. (a) The ana^sthesiating influence of chloroforra and ether is 

 most decided, both in the case of the naked- and of the covered- 

 eyed Medusaj. The first indications of approaching torpor are (a) 

 decrease in the rate of tlie pulsations and (f>) diminution of their 

 vigour. These indications rapidly become more and more marked, 



