"any legitimate analogy"

A richly-written speculation on extraterrestrial life from Richard Owen's 1849 biology text “On the Nature of Limbs” is found below; if he were talking of life in Earth he would be mentioning the phenomenon of convergent evolution, but in the case of non-Earth life we would be talking about a special case of parallel evolution, special because even in Earth life, parallel evolution ins among life that is somewhat related simply by the fact that all Earth life appears to have a common ancestor. Anyway, fascinating to note that today, SETI research is well-underway and the broader field of astrobiology is a well-funded and central field of many space research organizations, including NASA and the European Space Agency.

“The naturalist and anatomist, in digesting the knowledge which the astronomer has been able to furnish regarding [star and sunlight on other planets] can hardly avoid speculating on [the evolution of the light-sensitive organs such as eyes on other planets]...

[for example]...the laws of light, as of gravitation, being the same in Jupiter as here, the eyes of such creatures as may disport in the soft reflected beams of its moons will probably be organized on the same dioptric principles as those of the animals of a like grade of organization on this earth. And the inference as to the possibility of the vertebrate type being the basis of the organization of some of the inhabitants of other planets will not appear so hazardous, when it is remembered that the orbits or protective cavities of the eyes of the Vertebrata of this planet are constructed of modified vertebræ. Our thoughts are free to soar as far as any legitimate analogy may seen to guide them rightly in the boundless ocean of unknown truth.

And if censure be merited for here indulging, even for a moment, in pure speculation, it may, perhaps, be disarmed by the reflection that the discovery of the vertebrate archetype could not fail to suggest to the Anatomist many possible modifications of it beyond those that we know to have been realized in this little orb of ours.

The inspired Writer, the Poet and the Artist alone have been privileged to depict such.”