The doctrine of descent and Darwinism . yed by themale and female sexual organs is per-formed in the generative cycle of theCladonema by the sexual animals. Byfollowing the transition from the de-pendent organ into the independentanimal, we find the solution and ex-planation of the process termed he-terogenesis. Between the genera reproduced like theHydractinia, and those reproduced like the Cladonema,there are many others, of which the propagation showsthe gradual transition of the rudimentary sexual organsinto the sexual animal. We may so arrange the generaof the Medusa polypes as to exhibit
The doctrine of descent and Darwinism . yed by themale and female sexual organs is per-formed in the generative cycle of theCladonema by the sexual animals. Byfollowing the transition from the de-pendent organ into the independentanimal, we find the solution and ex-planation of the process termed he-terogenesis. Between the genera reproduced like theHydractinia, and those reproduced like the Cladonema,there are many others, of which the propagation showsthe gradual transition of the rudimentary sexual organsinto the sexual animal. We may so arrange the generaof the Medusa polypes as to exhibit how the partswhich in the Hydractinia are capsules, generatingand enclosing the ova, become more and more acquire a special branch of the alimentary canaland blood-vessels, and are provided with the marginalpapillse characteristic of the Medusas, and constitutingtheir peculiar sensory organs. In short, what in onemember of the systematic series may be termed anorgan, is, in the next, the Medusa separating itself and. Fig. 15. PARASITIC WORMS. 205 becoming a new generation; the sexual organ hasbecome tlie sexual animal. Now as the individual development of the Clado-nema, and other Medusae similarly propagated, corre-sponds with the systematic series of the Medusa polypes,the only reasonable and credible explanation of theontogenesis of those Medusae in which heterogenesisoccurs, is that, in them, the historical development ofthe genus has become fixed. Neither the egg northe hen were created. Before the delicately tintedMedusae populated the primaeval ocean in lonely splen-dour, the Medusa polypes on the constantly changingshores were the sole representatives of the still infantclass. Why single genera, like the Hydractinia, re-mained strictly conservative while others in variousdegrees paid homage to progress, whether and howthe struggle for existence and survival of the fittestwere here concerned, it is certainly impossible to provein the individual specie
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Keywords: ., bookauthorschmidtd, bookcentury1800, bookdecade1880, bookyear1882
