Page:Popular Science Monthly Volume 63.djvu/515

Rh peculiarly spotted form common to the Mediterranean and adjacent seas capable of liberating a charge that will shock man and must be destructive to hosts of smaller animals, upon which it is doubtless used as a means of offense and defense; in the electric siluroid of Africa, which in different structure possesses the same power in greater force, and still more pronouncedly in the electric eel of South America, the shock from which is sufficient to paralyze a horse. What strange combination of circumstances has conspired to develop such a power in these animals? Evidently some condition common to their several environments, as it must have originated independently in each of the examples cited. The difference in position and structure, though all are modified from muscular tissue, is such that no common origin can be assigned to the structure in the different forms.

In the adaptations to deep sea life we have one of the greatest extremes and, since we have here one of the most remarkable series of animals and moreover one which until recent years has been unknown to science, it will not be amiss to give it more than passing notice. In the greater depths of the ocean we have conditions rivaling those of caves in the absolute exclusion of light, but very different in the medium and in the enormous pressures to which the animals are here subjected—pressures so great that when deep sea animals are brought to the surface there is an expansion of all the soft parts, an extrusion of the eyes, stomach, etc., producing most monstrous looking forms. But the passage from moderate depths to deeper and deeper points and, finally, to the abysses of mid-ocean are gradual, and we can conceive a gradual pushing off to deeper and deeper points till enormous depths are reached. Even yet, however, it is believed that the deepest reaches are uninhabited and uninhabitable, the lowest points from which life forms have been secured being far above the extreme depths that are known.

The wonderful discoveries of the 'Challenger,' 'Albatross,' 'Blake' and other deep-sea explorations, adding a new chapter in science and whole new groups of animals hitherto unsuspected, are yet so fresh in the minds of those interested in such matters that they may well serve my purpose in illustrating those special adaptations reached by animals that have pushed into apparently inhospitable regions. The passage in this case has, however, been slow. We need assume no sudden change of physical conditions tending to produce modifications of structure, but practically unaltered physical conditions and a simply crowded condition of life forms in regions already occupied, as the main factor in pushing into this hinterland of habitable zones. Here as in caves we should expect the loss of light to result in the loss of eyes, but this is not always the case, for in some of these grotesque denizens of the deep instead of the loss of eyes we find the development of marvelous