Therefore, rather than permit a continuance of such encounters, I separated the crabs, and introduced them to companions more suited to the nature of each. The difference exhibited in the form and development of the tail in the ten-footed Crustacea (_Decapoda_)--as for instance, the crab, the lobster, and the hermit-crab--is so striking that naturalists have very appropriately divided them into three sections, distinguished by terms expressive of these peculiarities of structure: 1st, _Brachyura_, or short-tailed decapods, as the Crabs; 2d, _Anomoura_, or irregular tailed, as the Hermit-crabs; 3d, _Macroura_, or long-tailed, as Lobster, Cray-fish, &c. It is to a further consideration of a few familiar examples of the first mentioned group that I propose to devote the remainder of this chapter. Few subjects of study are more difficult and obscure than such as belong to the lower forms of the animal kingdom. However carefully we may observe the habits of these animals, our conclusions are too often apt to be unsound, from our proneness to judge of their actions as we would of the actions of men. As a consequence, an animal may be pronounced at one moment quiet and intelligent, and at another obstinate and dull, while perhaps, if the truth were known, it deserves neither verdict. For my own part, the more I contemplate the habits of many members of the marine animal kingdom, the more am I astounded at the seeming intelligence and purpose manifested in many of their actions. Prior, apparently, must have been impressed with the same idea, for he says, speaking of animals,-- "Vainly the philosopher avers That reason guides our deeds, and instinct _theirs_. How can we justly different causes frame _When the effects entirely are the same?_ Instinct and reason, how can we divide? 'Tis the fool's ignorance, and the pedant's pride!" This train of thought has been suggested to my mind by viewing the singular conduct of a Shore-Crab, whom I kept domesticated for many consecutive months. Three times during his confinement he cast his exuvium, and had become nearly double his original size. His increased bulk made him rather unfit for my small ocean in miniature, and gave him, as it were, a loblolliboy appearance. Besides, he was always full of mischief, and exhibited such pawkiness, that I often wished he were back again to his sea-side home. Whenever I dropped in a meal for my Blennies, he would wait until I had retired, and then rush out, disperse the fishes, and appropriate the booty to himself. If at all possible, he would catch one of my finny pets in his arms, and speedily devour it. Several times he succeeded in so doing; and fearing that the whole pack would speedily disappear, unless stringent measures for their preservation were adopted, I determined to eject the offender. After considerable trouble, his crabship was captured, and transferred to a capacious glass.