186. JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
tige of ganglia, but to descend at once to the 
lowest forms of animal and vegetable life, rhythmic 
action may here be said to be the rule rather than 
the exception. The beautifully regular motions 
observable in some Alogw, Diatomacez, and Ocilla- 
toriz, in countless numbers of Infusoria, Anthero- 
zoids, and Spermatozoa, in ciliary action, and even 
in the petioles of Hedysarum gyrano, are all in- 
stances (to which many others might be added) of 
rhythmical action where the presence of ganglia 
is out of the question. Again, in a general way, 
is it not just as we recede from these primitive 
forms of contractile tissue that we tind rhythmic 
action to become less usual? And, if this is so, 
may it not be that those contractile tissues which 
in the higher animals manifest rhythmic action are 
the contractile tissues which have longest retained 
their primitive endowment of rhythmicality? To 
my mind it seems hard to decide in what respect 
the beating of a Snail’s heart differs from that of 
the pulsatile vesicles of the Infusoria; and I do 
not think it would be much easier to decide in what 
essential respect it differs from the beating of the 
Mammalian heart. The mere fact that the presence 
of ganglia can be proved in the one case and not 
in the other, seems to me scarcely to justify the 
conclusion that the rhythm is in the one case 
wholly dependent, and in the other as wholly in- 
dependent, of the ganglia. At any rate, this fact, 
if it is a fact, is not of so self-evident a character 
as to recommend to us the current theory of gang- 
lionic action on @ priori grounds. 
