34  JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
other words, but for the sake of symmetry, I might 
as well have stated at the first that in the case of 
the covered-eyed Meduseze all the remarkable para- 
lyzing effects which are obtained by excising the 
entire margin of an umbrella are obtained in exactly 
the same degree by excising the eight lithocysts 
alone; the intermediate marginal tissue, in the case 
of these Medusee, is totally destitute of locomotor 
centres. 
Effects upon the Manubrium of excising the Margin 
of a Nectocalyx or Umbrella. 
Lastly, it must now be stated, and always borne 
in mind, that neither in the case of naked nor 
covered eyed Meduse does excision of the margin of 
a swimming organ produce the smallest effect upon 
the manubrium. For hours and days after the 
former, in consequence of this operation, has ceased 
to move, the latter continues to perform whatever 
movements are characteristic of it in the unmuti- 
lated organism—indeed, these movements are not 
at all interfered with even by a complete severance 
of the manubrium from the rest of the animal. In 
many of the experiments subsequently to be 
detailed, therefore, I began by removing the manu- 
brium, in order to afford better facilities for 
manipulation. 
Summary of Chapter. 
With a single exception to hundreds of observa- 
tions upon six widely divergent genera of naked- 
