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Show 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 projecting 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. III. THE SYSTEMATIC POSITION OF SPONGES. The opinions of different authors on this subject diverge considerably. 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 Haekel 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 established 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 |
