37G 



PROVISIONAL HYPOTHESIS 



Chai\ XXVII. 



Before proceeding to show, firstly, how far these assump- 

 tions are in themselves probable, and secondly, how far they 

 connect and explain the various groups of facts with which we 

 are concerned, it may be useful to give an illustration of the 

 hypothesis. If one of the simplest Protozoa be formed, as 

 appears under the microscope, of a small mass of homogeneous 

 gelatinous matter, a minute atom thrown off from any part and 

 nourished under favourable circumstances would naturally 

 reproduce the whole ; but if the upper and lower surfaces were 

 to differ in texture from the central portion, then all three 

 parts would have to throw off atoms or gemmules, which when 

 aggregated by mutual affinity would form either buds or the 

 sexual elements. Precisely the same view may be extended to 

 one of the higher animals ; although in this case many thousand 

 gemmules must be thrown off from the various parts of the 

 body. Now, when the leg, for instance, of a salamander is cut 

 off, a slight crust forms over the wound, and beneath this crust 

 the uninjured cells or units of bone, muscle, nerves, &c, are 

 supposed to unite with the diffused gemmules of those cells 

 which in the perfect leg come next in order ; and these as they 

 become slightly developed unite with others, and so on until a 

 papilla of soft cellular tissue, the " budding leg," is formed, and 

 in time a perfect leg. 30 Thus, that portion of the leg which had 



" we have two groups of physiological 

 " units, slightly different in their struc- 



" tures. 



»> 



" It is not obvious that 



" change in the form of the part, caused 



.- 



a 



.. 



.. 



built — only then can we count on a 

 complete transfer of the modification 



to descendants. 



>> 



• • • • 



"That the 



change in the offspring must, other 



" by changed action, involves such change " things equal, be in the same direction 

 " in the physiological units throughout *' 



" as the change in the parent, we may 

 " the organism, that these, when groups " dimly see is implied by the fact, that 

 " of them are thrown off in the shape of " the change propagated throughout the 

 " reproductive centres, will unfold into . " parental system is a change towards 



" organisms that have this part similarly 

 " changed in form. Indeed, when treat- 

 " ing of Adaptation, we saw that an 



u 



u 





a new state of equilibrium — a change 

 tending to bring the actions of all 

 organs, reproductive included, into 



" organ modified by increase or decrease " harmony with these new actions. 



y> 



" of function can but slowly so react on 



30 M. Philipeaux (' Comptes Rendus/ 



"the system at large as to bring about Oct. 1, 18GG, p. 576, and June, 1867) 



" those correlative changes required to has lately shown that when the entire 



" produce a new equilibrium ; and yet fore-limb, including the scapula, is ex- 



" only when such new equilibrium has tirpated, the power of regrowth is lost. 



' ' been established, can we expect it to be From this he concludes that it is neces- 



" fully expressed in the modified physio- sary for regrowth that a small portion 



" logical units of which the organism is of the limb should be left. But as in 







