228 STUDIES IN GENERAL PHYSIOLOGY 
volume of water contained in ordinary sea-water renders 
regeneration impossible, the same effect is not obtained until 
125 per cent. of fresh water has been added. 
IX. THE RELATION BETWEEN LONGITUDINAL GROWTH AND THE 
CONCENTRATION OF THE SEA-WATER IN TUBULARIA 
1. One searches modern text-books of physiology in vain 
for a chapter on growth; it scarcely exists even by title. 
So far as I have been able to judge from the literature, 
observations on the physiological conditions necessary for 
growth in animals have been exceedingly few. I will give 
here what I have been able to find. 
The oldest observations on the growth of animals are 
probably made by Bonnet, who was encouraged to do so 
through Hales’s work.’ Bonnet measured the growth of 
worms. The choice of material for these experiments was 
unfortunate, as the length of these animals is subject to 
great variations because of the contractions of the body. 
Bonnet measured with calipers “la plus grande longueur du 
ver,” and made these values the basis of his conclusions. 
He cut a worm into two, a second into four, a third into 
eight parts, etc., and tried to see whether the growth of the 
parts differed. His measurements showed ‘qu'il n’y a pas 
de différence considérable entre le progrdés que font dans le 
méme temps des moitiés et des quarts et ceux de huitiémes 
et de dixiémes” (p. 214); and further, ‘“‘que la derniére 
portion est celle de toutes qui, en temps égal, prend le moins 
d’accroissement, et aprés elle, celles qui la précédent immé- 
diatement.” It seems strange that the work of Bonnet stimu- 
lated no one to repeat his experiments upon more suitable 
material and with a better guarantee of accuracy. 
So far as I can determine, further experiments on the 
conditions for the longitudinal growth of animals have been 
1CHARLES BONNET, uvres d histoire naturelle et de philosophie, Vol. I, “Traité 
d'Insectologie ” (Neuchatel, 1779), p. 193. 
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