Page:Popular Science Monthly Volume 9.djvu/433

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409
WHAT ARE SPECIES?

as seen in c and d (Fig. 13). The coils grow closer together as the filament increases in size, until a hollow cylinder is formed. From the same threads below the base of the coil one or more processes grow out which are the male organs, and, where one of these threads reaches the tip of the female coiled filament, that organ is fertilized. From this time on, this body undergoes various and complicated changes, which finally result in a bright-yellow spherical body (Fig. 13, f), which consists of a thin wall inclosing a large number of sacs, g, each of which contains eight spores.

To find all these various stages of development is a matter of some time and patience; but nothing is more satisfactory in the study of moulds than to trace all these steps, from the first bending of the filament to the perfect sphere with its multitude of spores.

For a long time these two forms of fruit in the Aspergillus were considered as belonging to distinct and widely-separated species, but, when the microscope shows that they are produced from the same mycelium, it is time to conclude that they are but two methods of continuing the same species.

Space forbids further details concerning our common moulds; but it is hoped enough has been said to show that among them the species are distinct. The tiny forests which the microscope reveals are made up of forms as decided as those which compose our woodlands and groves. In closing, the reader expects an answer to the question which very naturally arises, viz., "What good do they do?" Though often of great annoyance in domestic and other affairs, yet all in all it is safe to say the good they accomplish far overbalances the harm. They are scavengers which do in their own inobtrusive way a vast amount of sanitary work. Though small in themselves, they are great reducing agents, striving to bring about that equilibrium so necessary to perfect harmony in the organic world. They hasten decay, tear down the accumulating rubbish around us, and allow the elements thus liberated to pass again into the cycle of ceaseless activity and growth.

To the thoughtful mind moulds do not simply excite wonder or disgust, but teach a deeper lesson of adaptation and service of little things, in the perfect and economical scheme of creation.

 

WHAT ARE SPECIES?
By Prof. T. H. HUXLEY.

IN its most general acceptation the word "species" signifies a kind or sort of something, which something is the genus to which the species belongs. Thus, a black stone is a species of the genus stone; a gray horse is a species of the genus horse; a scalene triangle is a species of the genus triangle; and, generally, it may be said that