1876 MEDUSAE 31 



tiated protoplasm. These strands are not sponta- 

 neously contractile, although their dimensions are 

 altered by the contraction of the muscular branch 

 on each of their sides. No part of the tissue is 

 doubly refracting in the fresh state. Is there any 

 way of treating it with a view of bringing out this 

 property if latent, so to speak ? The peculiarity is 

 not due to the transparency of the tissue, for I find 

 that the muscular fibre of the transparent osseous 

 fish Leptocephalus is as doubly-refracting as could be 

 wished. There are no signs of striae, but Agassiz 

 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 



