Sponges and Their Modes of Growth.

On Wednesday evening, Prof Alpheus Hyatt, of Technology, who was formerly connected with the U. S. fish commission, delivered a lecture on "Sponges" before the Natural History Society, in which he gave the results of his studies, some of which are as yet unpublished. He differs from many others in his classification, and in regarding sponges as individuals not as colonies. A sponge is essentially a globular sieve with the meshes prolonged into a labyrinth of minute tubes. Contrary to the general belief, sponges breathe by means of their outer layer. The inner layer consists of small cells armed with whips which create a current to draw in the small water animals which form its food. Between these two is another layer, which secretes the chalky, or horny, spicules which form the skeleton. All sponges are modifications of this simple form. Among the many specimens shown, one form deserves special mention, as it destroys many thousands of oysters every year. This kind perforates the shells by chemical action, and covers them entirely with its own substance. Another kind is a valuable substance for polishing powders.

The lecture was profusely illustrated with models, diagrams, and many beautiful specimens, and was much enjoyed by the audience on account of its freedom from technicalities and clear presentation of the subject.