But nothing in the lives of all these little nest-builders is more interesting than the intelligence they display and the facility with which they adapt themselves to circumstances. They seem to be able to grasp almost instantly the conditions of the environment, and to employ a wise discrimination in suiting them to their wants. Hardly two nests are alike. Marked differences in details of structure, configuration and surroundings are apparent, which prove that these creatures are controlled by reason, rather than instinct, in the elaboration of their homes. That they have some means of communicating their desires to each other cannot be doubted. When the male has laid hold of a stem, a pebble or a stick that completely baffles all effort at removal, his mate seems summoned to his assistance, and the united strength of the pair accomplishes the object to be gained. There is ever noticeable in whatever the sexes undertake some concert of action which would put to shame the boasted intelligence of man himself. The Sun-fishes, as has been said, nest in companies. When the combined effort of two individuals is unable to expel an invader, the entire community, as by a single mighty impulse, rises up against the foe. There is evidence of some form of society, even though simple in its organization, where individual members league themselves together for mutual protection and defence. Other examples might be cited to give the reader a common-sense estimate of the comparatively high order of intelligence that characterizes the actions of many of our fishes. SLIPPERY AS AN EEL. Eels are found in almost all warm and temperate countries, and grow to a very great size in tropical regions. They are impatient of cold, and hence do not exist in the extreme northern and southern parts of the world. In many islands of the Pacific Ocean they are held in considerable estimation, being preserved in ponds and fed by hand, but in many civilized communities a strong prejudice prevails against them, probably from their similarity to snakes, which prevents even a hungry man from caring to eat such wholesome and nutritious food. Not one of our river fishes is so mysterious as the Eel, and although much is now known that was involved in obscurity, yet there is still much to learn of its habits, especially the manner of its reproduction. Difference of locality, it is likely, may influence the Eel and cause a difference of habit, an opinion which seems warranted from the various and perplexing accounts that have been given of its customs by numerous practical observers.