30 THE AQUARIAN NATURALIST. 



In their natural state the Sponges are soft and 

 elastic, and some of them are tinted with lively 

 colours ; but many of the species, by drying, become 

 quite friable, lose their fine shades of colour, and 

 grow white. Soon after death they pass through a 

 bluish colour to black, in consequence of putrefac- 

 tion ; and when this occurs, we need hardly say, the 

 more speedily they are removed from the aquarium 

 the better. 



They seem to grow best near the shore ; yet even 

 Aristotle speaks strongly of the injurious effects of 

 high temperature on these animals, and says that it 

 causes them to run rapidly to putrefaction, a remark 

 which any of our readers who may be desirous of 

 keeping sponges alive will find it useful to remember, 

 more especially as the same remark is equally appli- 

 cable to a vast number of the humbler zoophytes. 



It would hardly be supposed by any casual observer, 

 that beings apparently motionless and inactive as the 

 rocks on which they grow, should possess much in- 

 terest beyond what attaches itself to their variety of 

 form and delicacy of structure, and yet few creatures 

 exhibit phenomena more wonderful. 



" In the month of November," says Professor Grant, 

 " I put a small branch of the Spongia coalita (PI. I. 

 fig. 1, ), with a little sea-water, into a watch-glass, 

 and placed it under the microscope; when, on re- 

 flecting the light of a candle up through the fluid, I 

 soon perceived that there was some movement going 

 on among the opaque particles floating through the 

 water. On moving the watch-glass so as to bring 

 one of the apertures on the side of the sponge fully 



