The substance exists in such minute amounts that thus far it has been impossible to isolate it in anything approaching a pure form. The Virginia biologists have set themselves a task requiring infinite patience over many years—tracing the increase of the amount in the salivary glands of each individual through each of its fourteen lives, and also through the eggs with which the strange life cycle starts. The present clues indicate that the substance is a filterable virus—tiniest of living things compared with which the pinhead-sized aphis is like a whale compared to a fly. _Shyness Characteristic of Giant Rats_ Biggest of the extant true rats is the giant rat of Liberia. It is two feet or more in length and is similar in appearance to the Norway rat which infests houses all over the world. Fortunately this creature never has invaded the homes of men. It is a shy animal of the cane brakes. _Nocturnal Potto_ One of the weirdest of living mammals is the potto—“ghost monkey”, of West African jungles. It is about the size of a squirrel, with soft, yellow fur and protruding yellow eyes which shine like malevolent witch lights in the darkness of the jungle nights. The potto is a nocturnal animal of the tree tops. Its weird, whimpering cries are believed by natives to be the voices of evil spirits. The little creature is an aberrant member of the family of lemurs, ancient offshoots of the same family from which sprang the monkeys and great apes. _Where Trees are Square_ A few miles north of the Panama Canal Zone is “the valley of square trees.” This is the only known place in the world where trees have rectangular trunks. They are members of the cottonwood family. Saplings of these trees now are being grown at the University of Florida to find out if they retain their squareness in a different environment. It is believed, however, that the shape is probably due to some unknown but purely local condition. That the cause is deep-seated is indicated by the fact that the tree rings, each representing a year’s growth, also are square. _The Lamp That is a Beetle_ The most brilliant animal luminescence known is that of the carbuncle beetles of Puerto Rico. They emit a light so brilliant that one or two inside an inverted tumbler illuminate a room of moderate size so that one can read a newspaper at night. Fields are illuminated brilliantly every night by these beetles, flying about a foot above the ground. The light is not intermittent, and seems nearly continuous. It varies from yellow to green for different species; occasionally it is yellowish-red. _Rainstorms of Worms_