1875.] Locomotor System of Medusa. 149 



definite lines of discharge being present in the swimming-organs of 

 Medusae. I have hitherto failed, however, to detect any such lines histo- 

 logically. 



(b) After the waves have become completely blocked in a contractile 

 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 again 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 

 lines of discharge being present. I think, however, that there is a 

 theory by which these facts admit of being satisfactorily reconciled with 

 that supposition. But this whole subject awaits further and extensive 

 investigation. 



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

 causes blocking of the waves at that line. If the pressure be slight, the 

 blocking will be temporary ; but if severe or long-continued, 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. 



V. Additional Facts tending to show the identity of the Locomotor Centres 

 of Medusae with Nervous Tissue in general. 



§ 1. Having placed several hundred Sarsia in a large bell-jar, I com- 

 pletely 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 Sarsia were swimming. From 

 all parts of the bell-jar the Sarsia 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 individuals 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 exclu- 

 sively 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 numerous occupants 

 approached the heated metal. Therefore the rays by which the Sarsia had 

 been affected in the previous experiment were the properly luminous rays, 

 and not the calorific ones. 



§ 2. (a) The ansesthesiating influence of chloroform and ether is most 



