The yucca or Spanish bayonet and the century-plant, or American aloe (_Agave americana_), are thorny and spiny; they are also very woody and fibrous; yet nothing eats them or could eat them. They are no more edible than cordwood or hemp ropes. This fact alone settles the defense question about spines. V. SEA-DOGS There is a bit of live natural history out here in the sea in front of me that is new and interesting. A bunch of about a dozen hair seals have their rendezvous in the unstable waves just beyond the breakers, and keep together there week after week. To the naked eye they seem like a group of children sitting there on a hidden bench of rock, undisturbed by the waves that sweep over them. Their heads and shoulders seem to show above the water, and they appear to be having a happy time. Now and then one may be seen swimming about or lifted up in a wall of green-blue transparent water, or leaping above the wrinkled surface in the exuberance of its animal spirits. I call them children of the sea, until I hear their loud barking, and then I think of them as dogs or hounds of the sea. Occasionally I hear their barking by night when it has a half-muffled, smothered sound. They are warm-blooded, air-breathing animals, and there seems something incongruous in their being at home there in the cold briny deep--badgers or marmots that burrow in the waves, wolves or coyotes that hunt their prey in the sea. Their progenitors were once land animals, but Darwinism does not tell us what they were. The whale also was once a land animal, but the testimony of the rocks throws no light upon its antecedents. The origin of any new species is shrouded in the obscurity of whole geological periods, and the short span of human life, or of the whole human history, gives us no adequate vantage-ground from which to solve the problem. I can easily believe that these hair seals are close akin to the dog. They have five digits; they bolt their food like dogs; their sense of smell is said to be very acute, though how it could serve them in the sea does not appear. The young are born upon the land and enter the water very reluctantly.