30 GEOEGE JOHN EOMANES 1875- 



says that in some of the Mediterranean species striae 

 are well marked. But if both striated and unstriated 

 fibres are elsewhere doubly-refracting, it does not, I 

 suppose, much signify whether or not the muscles of 

 Medusae are striated — so far, I mean, as the pecu- 

 liarity in question is concerned. 



I wish you would say what you think about this 

 peculiarity in relation to a subject that I have been 



working up. You no doubt remember that in 's 



paper that we heard read, he said that the snail's heart 

 had no nerves or ganglia, but nevertheless behaved 

 like nervous tissue in responding to electrical stimula- 

 tion. He hence concluded that in undifferentiated 

 tissue of this kind, nerve and muscle were, so to 

 speak, amalgamated. Now it was principally with 

 the view of testing this idea about ' physiological 

 continuity ' that I tried the mode of spiral and other 

 sections mentioned in my last letter. The result of 

 these sections, it seems to me, is to preclude, on the 

 one hand, the supposition that the muscular tissue of 

 Medusae is merely muscular (for no muscle would 

 respond to local stimulus throughout its substance 

 when so severely cut), and, on the other hand, the 

 supposition of a nervous plexus (for this would 

 require to be so very intricate, and the hypothesis of 

 scattered cells is without microscopical evidence here 

 or elsewhere). I think, therefore, that we are driven 

 to conclude that the muscular tissue of Medusae, 

 though more differentiated into fibres than is the 

 contractile tissue of the snail's heart, is, as much as 

 the latter, an instance of 'physiological continuity.' 

 (Whether or not the interfascicular protoplasmic 



