354 LAMARCK, HIS LIFE AND WORK 
matic is an effort.’ Hence he regards effort as the 
immediate source of all movement, and considers that 
the control of muscular movements by consciousness 
is distinctly observable; in fact, he even goes to the 
length of affirming that reflex acts are the product of 
conscious acts, whereas it is plain enough that reflex 
acts are always the result of some stimulus. 
Another case mentioned by Lamarck in his Azz- 
maux sans Vertébres, which has been pronounced as 
absurd and ridiculous, and has aided in throwing his 
whole theory into disfavor, is his way of accounting 
for the development of the tentacles of the snail, 
which is quoted on p. 348. 
This account is a very probable and, in fact, the 
only rational explanation. The initial cause of such 
structures is the intermittent stimulus of occasional 
contact with surrounding objects, the irritation thus 
set up causing a flow of the blood to the exposed 
parts receiving the stimuli. The general cause is the 
same as that concerned in the production of horns 
and other hard defensive projections on the heads of 
various animals, 
In commenting on this case of the snail, Professor 
Cleland, in his just and discriminating article on 
Lamarck, says: 
‘“ However absurd this may seem, it must be ad- 
mitted that, unlimited time having been once granted 
for organs to be developed in series of generations, 
the objections to their being formed in the way here 
imagined are only such as equally apply to the the- 
ory of their origin by natural selection. =) win 
judging the reasonableness of the second law of 
