414 FUNCTIONS OF THE NERVES. [ch. hi. 



microscope enables us to detect only a granular mass, but 

 no muscle, no bones, no vessels, no nerves ; if, more- 

 over, there are vegetables, and portions of vegetables, which 

 display no doubtful irritability, and yet cannot be suspected of 

 containing muscles and nerves, it does not, therefore, follow, 

 that the irritability of muscles is not produced by the mechan- 

 ism described above ; it does follow, however, that that irrita- 

 bility, which in the greater and more perfect animals ought to 

 be adapted to the development of greater strength, is neces- 

 sarily dependent on the mechanism described by me ; while, 

 again, irritability in plants and polypes is not so powerful, and 

 can be produced by the Author of Nature by another and dif- 

 ferent mechanism than that of muscles. If this appear incre- 

 dible to any one, let him reflect that the function of generation 

 is more widely extended than irritability, yet, nevertheless, that 

 Nature accomplishes it, not in one way always, but by many 

 and by the most varied methods. Some animals are viviparous, 

 others oviparous ; and of these latter some have the ova fecun- 

 dated by the male after extrusion from the female, and some 

 before extrusion ; some incubate their ova, some abandon them 

 to be incubated by others ; some deposit fecundated ova, 

 without the coitus of the sexes ; some propagate by shoots ; the 

 polypus tintinabuliformis is reproduced by dividing its body 

 into two ; ^ the poh^pus plumosus propagates both by shoots and 

 by ova, which are always fecundated without coitus. 2 Why, 

 then, might not nature be able to produce irritability by dif- 

 ferent mechanisms — in muscles by the method described by 

 me — and in polypes, zoophytes, and plants, devoid of muscular 

 fibre, in some other way as yet unknown ? I am persuaded 

 that these things being weighed, my theory of muscular con- 

 traction is very near the truth; and I should be much delighted 

 if any attempts of mine should avail anything in elucidating 

 such a difficult subject, since I am not ignorant of the very 

 great anxiety of very learned men to understand the cause of 

 muscular contraction ; who to this end have not only spared 

 no labour, but have also endeavoured to stimulate other in- 

 quirers by great and most honorable rewards to perfect this 



• Spallanzani Opus. Physique, Tom. i, tab. i, fig. vii. (This figure represents a 

 vorticella. — Ed.) 

 '^ lleaumur. 



