22 THE MICROSCOPE. Feb- 



111 our collection of slides we have of course spicules 

 of sponges, and this seems generally to satisfy us. It 

 cannot be said that a sponge in its natural condition is 

 an object of beauty or should in any way attract an am- 

 ateur microscopist. We should therefore be thankful to 

 those patient investigators who extract, by perseverant 

 labors, interesting knowledge from nature, as bees gather 

 honey fri)m flowers. To taste these sweets I have con- 

 sulted Kent, Carpenter and the Cyclop. Brit. 



Classification. — The exact classification of sponges 

 has not yet been definitely agreed upon. Prof. Haeckel 

 insists to place them with the Coelenterata, and as a close 

 relative of the Corals, mainly because he claims for them 

 an ectoderm and endoderm and a true process of sexual 

 generation by germ cells becoming fertilized by sperm 

 cells, which latter claim is affirmed by Carpenter. Kent, 

 however, very forcibly denies both of these claims, finds 

 neither ectoderm nor endoderm, nor any indication of 

 sexual generation ; and therefore allies sponges with the 

 Choano-Flagellates or funnel-shaped flagellate inf usorias 

 as classified by him. Sponges are generally divided into 

 four classes according to the nature of their skeletons or 

 spicules. 1. Calcareous sponges having spicules of car- 

 bonate of lime. 2. Silicious sponges, which exist in the 

 greatest number, having silicious spicules. 3. Keratose 

 or horny sponges, being the sponges of commerce. 4. 

 Gelatinous sponges in which all spicules are absent. All 

 sponges, however, no matter what their skeleton, are 

 composed of a soft slimy sarcode forming the body, cov- 

 ering the exterior as well as the base of the interior 

 canals, ducts and cavities and forming a connective tis- 

 sue, showing, however, no fibres. 



Structure. — All sponges from the most simple to the 

 most complex have the same special characteristics to a 

 greater extent perhaps than any other class of beings. 

 Just as each species can be clearly defined from the 



