the Rotifers is prevented by the presence of a small quantity of moss, or of dirt—between the particles of which they find shelter—that they revive on the application of water. And even in the severe experiments of M. Doyère and M. Gavarret, some of the animals must have been thus protected; and I call particular attention to the fact that, although some animals revived, others always perished. But if the organization of the Rotifer, or Tardigrade, is such that it can withstand desiccation—if it only needs the fresh applications of moisture to restore its activity—all, or almost all, the animals experimented on ought to revive; and the fact that only some revive leads us to suspect that these have not been desiccated—a suspicion which is warranted by direct experiments. I believe, then, that the discrepancy amounts to this: investigators who have desiccated the moss containing animals, find some of the animals revive on the application of moisture; but those who desiccate the animals themselves, will find no instances of revival.]
The time spent on these Rotifers will not have been misspent if it has taught us the necessity of caution in all experimental inquiries. Although Experiment is valuable—nay, indispensable—as a means of interrogating Nature, it is constantly liable to mislead us into the idea that we have rightly interrogated, and rightly interpreted the replies; and this danger arises from the complexity of the cases with which we are dealing, and our proneness to overlook, or disregard, some seemingly trifling condition—a trifle which may turn out of the utmost importance. The one reason why the study of Science is valuable as a means of culture, over and above its own immediate objects, is that in it the mind learns to submit to realities, instead of thrusting its figments in the place of realities—endeavours to ascertain accurately what the order of Nature is, and not what it ought to be, or might be. The one reason why, of all sciences, Biology is pre-eminent as a means of culture, is, that owing to the great complexity of all the cases it investigates, it familiarizes the mind with the necessity of attending to all the conditions, and it thus keeps the mind alert. It cultivates caution, which, considering the tendency there is in men to "anticipate Nature," is a mental tonic of inestimable worth. I am far from asserting that biologists are more accurate reasoners than other men; indeed, the mass of crude hypothesis which passes unchallenged by them, is against such an idea. But whether its advantages be used or neglected, the truth nevertheless is, that Biology, from the complexity of its problems, and the necessity of incessant verification of its details, offers greater advantages for culture than any other branch of science.
I have once or twice mentioned the words Mollusc and Crustacean, to which the reader unfamiliar with the language of Natural History will have attached but vague ideas; and although I wanted to explain these, and convey a distinct conception of the general facts of Classification, it would have then been too great an interruption. So I will here make an opportunity, and finish the chapter with an indication of the five Types, or plans of structure, under one of which every animal is classed. Without
