CHAPTER XIII. 



REPRODUCTION AND DEVELOPMENT IN THE INVERTEBRATA. 



Every living organism possesses the power of reproducing 

 its kind. The process by which this reproduction or pro- 

 creation is maintained may be either asexual or sexual; and 

 some scientists* assert a third mode of " reproduction " — viz., 

 by spontaneous generation, abiogenesis, or heterogenesis, i.e., 

 the origin of living organisms de novo, without parents. It is 

 not our object to discuss the arguments for and against the 

 theoiy of spontaneous generation, suffice it to say that the 

 researches of Pasteiir, Tyndall, Dallinger, and others, point 

 out that " no definite instance of life originating de novo has 

 been proved," and their experiments appear to negative its 

 possibility.! Yet, it has been stated that the facts adduced 

 against the theory '' do not appear to invalidate the possibility 



* See Dr. Bastian's Bef/mninys of Life (1872) ; Bennett's Physiolotjij, 

 p. 421 ; Pouchet's NouveUes Exptriences sur la Generation Spontanee et sin- 

 la litsisUmce Vitale, p. no; and also the works of Prof. P. Mantegazza 

 and MM. Bernard, Pennetier, Joly, and Musset. 



t Concerning the controversy on spontaneous generation, Prof. Hnxley 

 states that biogenesis (life from previous life) has been "victorious along 

 the whole line;" but at the same time he remarks "that with organic 

 chemistry, molecular physics, and physiology yet in their infancy, and 

 every day making prodigious strides, it would be the height of presumption 

 for any man to say that the conditions under which matter assumes the 

 qualities called vital, may not some day be artificially brought together." 

 And further the great biologist remarks, " that as a matter not of proof but 

 of probability, if it were given me to look beyond the abyss of geologically 

 recorded time, to the still more remote period when the earth was passing 

 through chemical and physical conditions, whict it can never see again, I 

 should expect to be a witness of the evolution of living protoplasm from 

 non-living matter." 



