216 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



force, or magnetic force, or od-force, to account for the existence of a mass of phenomena 

 which will not arrange themselves under any of his established categories — forgetting that 

 a " force," the conditions of whose operation (that is, whose laws) are undetermined, is hut 

 a scientific idol, at once empty and mischievous, — empty, because it is but a phrase with- 

 out real meaning ; mischievous, because it acts as an intellectual opiate, confusedly satis- 

 fying many minds and obstructing the progress of inquiry into the real laws of the 

 phenomena. If we shoAv that a fact is a case of a law, we explain that fact ; but expla- 

 nation by reference to an undefined " force," of questionable existence, is simply ' ignorance 

 wi'it large.' 



Now, how does the hypothesis fulfil the incUspensable conditions of a genuine explana- 

 tion? In the first place, what proof is there of the existence of such a force as " sper- 

 matic force." All that we loioio is, that an ordinary ovum will not undergo those changes 

 which constitute development without the contact of the spermatozoon. Hence it is 

 concluded that some force contained in the spermatozoon is the efficient cause of all these 

 changes. But what would be thought of the artillerist who should imagine he had ex- 

 plained the propulsion of a bullet by saying it was ' trigger force ' ? Or to take an 

 illustration from phenomena of a like order to those under discussion : a seed wiU not 

 grow tvnless it is exposed to a certain amount of warmth and moisture; btit have I 

 explained the growth by saying that it is the eff'ect of ' heat and moisture force ' which 

 becomes diffused through the seed ? 



The very existence of this " spermatic force," then, is a gratuitous assumption; and if 

 we seek for its laws of action, we fiiid but two stated : first, that it becomes weakened by 

 the successive divisions of the germ-cell ; second, that " the force is exhausted in pro- 

 portion to the complexity and living powers of the organism developed from the primary 

 germ-cell and germ-mass." 



I have shown to what singular consequences the first assumption leads us ; it remains 

 only to consider the second. If it be true, the occurrence of agamogenesis in the animal 

 kingdom must bear an approximatively inverse ratio to the complexity of the organization 

 of the different groups. Let us examine one or two subkingdoms in this point of view. 

 Among the Aimulosa, the Rotifera and Turbellaria possibly possess it to a small extent ; 

 the Nematoidea do not possess it at all. Many Trematoda possess it ; others, such as 

 Aspidogaster, have nothing of the kind. The Accmthocephala are not known to possess it ; 

 the Eclibiodermata are regarded by Prof. Owen as possessing it, but theu* different families 

 show every gradation from simple metamorphosis to something like agamogenesis. A few 

 Annelida possess the power in a marked degree ; in many, nothing of the kind is known. 

 The Nais has it ; the Earth-worm and the Leech have it not. Of the Crustacea, some, 

 such as many BrancJdo])oda, exhibit it in the highest perfection ; but no trace of it has 

 yet been found in Copejioda, Cirripedia, Pcecilopoda, Edriop)hthalniia, or Fodophthalmia. 

 In the 3Iyriapoda and Arachnida the process is not known : but we find it in the highest 

 Articulata — ^the Insecta — and this not, so far as we know at present, in Aptera or Ortlio- 

 ptera, but in a few Hemiptera, Hymenoptera and Lepidoptera ; and there is every reason to 

 believe that it only occurs in isolated, though perhaps in many, genera of these orders. Take 

 the Mbllusca again : agamogenesis occurs in the Folyzoa and Ascidioida, not in the Bra- 



