It has been before stated that some of the zoophytes may be mounted dry, and others examined as opaque or transparent objects according to their substance. They are very interesting when examined in the trough whilst living, but to preserve many of them for future examination they must be mounted in some preservative medium. Sometimes this may be one of the liquids mentioned in Chapter IV., but if possible they should be kept in balsam, as there is less danger of injury by accident to this kind of slide. This method of mounting presents some difficulties, but I think that all agree as to the trustworthiness of Dr. Golding Bird’s information on the subject, which appeared in the _Microscopic Journal_. Of this, space forbids me to give more than a condensed account, but I hope to omit nothing of moment to the reader for whom these pages are written. After stating that there are few who are not familiar with these exquisite forms, and have not regretted the great loss of beauty they sustain in dying, he informs us that from their so obstinately retaining air in the cells and tubes when dried, it is hardly practicable to get rid of it; and they also shrivel up very seriously in the process of drying. The following plan, however, he has found almost faultless in their preparation. To preserve them with extended tentacles, they should be plunged in cold fresh water, which kills them so quickly that these are not often retracted. The specimens should be preserved in spirit until there is leisure to prepare them; if, however, they have been _dried_, they should be soaked in cold water for a day or two before being submitted to the following processes:-- 1. After selecting perfect specimens of suitable size, immerse them in water heated to about 120° and place them under the receiver of an air-pump. Slowly exhaust the air, when bubbles will rise and the water appear to be in a state of active ebullition. After a few minutes re-admit the air and again exhaust, repeating the process three or four times. This will displace the air from most, if not all, of the class. 2. Remove the specimens and allow them to drain upon blotting-paper for a few seconds; then place them in an earthen vessel fitted with a cover, and previously heated to about 200°. This heat may be easily got by placing the vessel for a short time in boiling water, wiping it immediately before use with a thick cloth. The specimens are then dropped into this, covered with the lid, and immediately placed under the receiver of the air-pump, and the air rapidly exhausted. By this means they are dried completely, and so quickly that the cells have no time to wrinkle.