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It is now generally held that species blend or have blended into one another; so that any possibility of arrangement and apparent subdivision into definite groups, is due to the suppression by death both of individuals and whole genera, which, had they been now existing, would have linked all living beings by a series of gradations so subtle that little classification could have been attempted.
London Clay, Sheppey. Natural size. a. Cone. b. Carruthers, having examined the original specimens now in the British Museum, tells me that all these cones from Sheppey may be reduced to two species, which have an undoubted affinity to the two existing Australian genera above mentioned, although their perfect identity in structure can not be made out.
Moreover, the hypothesis, in claiming that a heterogenetic generation of one species from another must necessarily nullify all similarity between the organism of the child and that of the mother, is so little convincing, and shows in the necessity of conceiving the universal type of organisms, the type of kingdoms, of main types, of classes, of orders, of families, of genera, and of species, as but individual existences which, in the form of cells and before the existence of the developed species, partly through many thousands of years, lead a real empiric and concrete life such an abstract synthetical construction of nature, that we are not astonished that the theory of the genealogy of primordial cells stands almost alone.
Thus every gradation, from an ordinary fixed spine to a fixed pedicellariae, would be of service. In certain genera of star-fishes these organs, instead of being fixed or borne on an immovable support, are placed on the summit of a flexible and muscular, though short, stem; and in this case they probably subserve some additional function besides defence.
Species of different genera and classes have not changed at the same rate, or in the same degree. In the oldest tertiary beds a few living shells may still be found in the midst of a multitude of extinct forms. Falconer has given a striking instance of a similar fact, in an existing crocodile associated with many strange and lost mammals and reptiles in the sub-Himalayan deposits.
The closely allied species also of the larger genera apparently have restricted ranges, and in their affinities they are clustered in little groups round other species in which respects they resemble varieties. These are strange relations on the view of each species having been independently created, but are intelligible if all species first existed as varieties.
For the rest, if it is difficult to reconstitute except in imagination the different stages through which, in time, and in a determined species, acts at first imperfect, but designed, have become perfect and instinctive, we can at least find in space different degrees of the same instinct in allied genera which lead us by a succession of transitions from mechanical action to reflective action.
Taking them therefore in mass, and unexamined, it required only a decent apprenticeship in logic, to draw forth their contents in all forms and colours, as the professors of legerdemain at our village fairs pull out ribbon after ribbon from their mouths. And not more difficult is it to reduce them back again to their different genera.
Dawson, in 1859, enumerated 32 genera and 69 species which he had then obtained from the State of New York and Canada. But fortunately the coal formation is fully developed on the other side of the Atlantic, and is singularly like that of Europe, both lithologically and in the species of its fossil plants.
The unimpregnated bloom falls off at its appointed date, as everybody knows; but if fertilized it remains entire, saving the labellum, until the seed is ripe, perhaps half a year afterwards but withered, of course. Very singular and quite inexplicable are the developments that arise in different genera, or even species, after fertilization.
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