564 DR. R. VON LENDENFELD ON THE SYSTEMATIC [DeC. 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). 



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. 



Epidermulia. 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. 



III. The Systematic Position of 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 



