564 DR. R. VON LENDENFELD ON THE SYSTEMATIC [Deec. 21, 
These pages will give a key to the terms of spicules used below. 
There are, however, a number of other terms which require 
explanation. 
The spicules are divided generally into two distinct groups :— 
(1) Those which together form the supporting skeleton of the 
sponge: these are called Supporting spicules or Megasclera. 
(2) Those which lie scattered in the ground-substance and which 
differ from the former in shape: these are called Flesh-spicules or 
Microsclera (Tension-spicules of Bowerbank). 4 
F. E. Schulze (1369) uses particular terms for spicules according 
to their position, which have been adopted in this paper so far as 
the Hexactinellids are concerned. 
These are alphabetically the following :— 
Autodermalia. Spicules on the outer surface with free projecting 
and with centripetal (immersed) differentiated rays. 
Autogastralia, Spicules on the gastral surface with free pro- 
jecting and with centrifugal (immersed) differentiated rays. 
Basalia. Spicules of the root-tuft. 
Comitalia. Spicules accompanying the fibres. 
Epidermalia. Spicules on the outer surface with free projecting 
differentiated ray only. 
Epigastralia. Spicules on the gastral surface with free projecting 
differentiated ray only. 
Hypodermalia. Spicules of the outer surface with immersed 
radial ray only.—Pentact. 
Hypogastralia. Spicules of the gastral surface with immersed 
radial ray only.—Pentact. 
Marginalia, Spicules forming a collar round the osculum. 
Parenchymalia. Spicules in the interior. 
Pleuralia. Spicules forming a fur. 
Principalia, Spicules of the main skeleton. 
Ill. Tur Systematic Posirion or SPONGEs. 
The opinions of different authors on this subject diverge con- 
siderably. I shall attempt to reconcile them in the following pages 
and to prove the correctness of the result at which I have arrived. 
Aristotle first pointed out that the Sponges were not plants—a fact 
which seems clear enough now, but which was doubted and combated 
by most authors of the dismally ignorant middle ages. This we 
admit as proved. I agree with Hackel in dividing the organic world 
into the three groups—Plants, Protista, and Animals. Among the 
Protista there are a great majority of forms showing affinities either 
to animals or to plants, so that it is not unusual to split up the 
Protista and divide its members among the two other old estab- 
lished groups. For the sake of simplicity I adopt this course 
here. 
The Animal Kingdom, in this wider sense, including the animal 
Protista, is naturally to be divided into Protozoa and Metazoa, of 
