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A UTHORS INVESTIGA TIONS. 1 4 1closely identical in character with the artificially prepared infusions of hay,and other vegetable substances, which are so speedily attended by theirmyriad guests. Their purpose in life, as in the case of the animalculesinhabiting artificial infusions, is to break down and convert into newprotoplasmic matter this otherwise waste product. To maintain the balancehere, however, and to check the too rapid increase of the herbivorousmonads, we find other types, such as Dinomonas and various Ciliata,answering to the Carnivora among the various higher animal sub-kingdoms,developed side by side with and feeding in turn upon the plant-eatingspecies.The general conclusions deducible from the long arrayof evidence nowproduced with respect to the question of "spontaneous generation," or"abiogenesis," may now be briefly summarized. From every line of inquiryreturned. Life in itsinvestigated, one and the same answer is invariablymost humble and obscure form, be it existent as impalpable germinal dustfloating inthe atmosphere, or shaken from a truss of hay, or manifested inits more active state as the minute monads, bacteria, and other organismsdeveloped in infusions, tells everywhere the same unvarying tale. Tracedbackwards to its origin, or forwards to its ultimate development, eachtype is found by patient search to be derived, not de novo out of dead orinorganic elements, but from a specific parental form identical in all respectswith itself, and whose life-cycle is as true and complete as that, even, ofman himself.To the scientific mind the conception that organic matter was primarilyeliminated, or in other words created, out of the inorganic, is forced homeas a natural and logical conclusion, and also that this transition may be aprocess of every day occurrence. So far, however, as such recurring or denovo generationis exhibited by the types of organic life dealt with inthis volume, or at present known, there is no longer left a loophole fordoubt. The evidence from all sides, revealed by the exhaustive light ofrecent research, proves conclusively that in all these cases, down to thelowest monad and bacterium, the reproduction of their kind, formerlysupposed to be altogether fortuitous and irregular, conforms in every essentialparticular with that of the highest members of the organic series.Accepting, in point of fact, the infusorial or protozoic spore as thephysiological, though not morphological, equivalentof the ovum of allhigher animals, or Metazoa, Harvey's once famous, but since discarded,aphorism " Omne vivum ex ovo," is found, so far as human knowledge hasas yet penetrated, to dominate with equal force from one extremity to theother of nature's chain. To assert, however, that we have penetrated toand laid bare the ultimate and finite confines of the organic realm, wouldbe an arrogant and altogether illogical assumption: a vast terra incognitaof organic forms may still remain to be explored. As yet, the latestinvestigations of physiologists have pushed so far forward as to acquire anapproximate, though by no means exhaustive, knowledge of the " cellular "