&1 '/' 



2 STYLASTERIDAE 



studied. It was thus of the highest importance to examine the soft parts of the northern Hydro- 

 corallines more thoroughly; as Pax correctly remarks in a recent work on stony corals (1910 p. 65), "wir 

 diirfen tins nicht verhehlen, dass jede Art, von der nur das Skelett vorliegt, als unvollstandig bekannt 

 gelteii muss, gleichgiltig, ob ihr anatomischer Ban fitr systematische Zwecke verwendbar ist oder nicht." 

 It appears from the investigations, that the least injurious solution with which to remove the 

 calcareous constituents is that recommended by Pax (1910 p. 71): 100 parts 70% alcohol, 10 parts con- 

 centrated nitric acid and 2 parts concentrated, aqueous phloroglucine solution. In small pieces of the 

 colony the calcareous parts are usually completely removed during about 12 hours; larger pieces have 

 sometimes to remain in the liquid up to 48 hours before all the carbonate of lime is removed. The 

 coarser structure is then studied most easily by means of thick celloidin sections, the finer by means 

 of thin paraffin sections. The staining methods depend in part on the fixation. In most cases I have 

 obtained excellent pictures on staining with haematoxylin and counterstaining with cosine or picric- 

 acid-fuchsine (van Giesson's). It is of interest to note, that the structureless organic tissue, which 

 intersects the skeleton in all directions, is coloured very intensely by the cosine and acid-fuchsine 

 in the same way as the supporting lamellae of the zooids, whilst the picric acid does not affect it in 

 van Giesson's staining method. - 



I cannot refrain from dwelling a moment here on the mineralogical composition of the skeleton. 

 Pax has investigated the skeleton of Flabellum inconstans and found, that it consists of aragonite. 

 He also brings together (1910 p. 70) the results of previous investigations in the same direction. Ac- 

 cording to his summary calcite has been determined as skeleton in Corallium, his, Tubipora, Cysti- 

 phyllum and A nabacia, whilst aragonite has been found in the following genera of Coelenterates : 

 Heliopora, Monlipora, Echinopora, Distichopora, Madrepora, Stylopora, Pocilopora, Millepora, Seriatopora, 

 Goniastraea, Podobacea, Galaxea, Fungia, Dendrophyllia, Forties, Astroides, Hydnophora, Sclerohelia, 

 Coeloria, Pterogyra, Merulina, Favia, Stylus ter and Trachypyllum. -- At my request the assistant at the 

 Geological Institute of the Polytechnic High School in Trondhjem, Dr. C. W. Carstens, has examined 

 the skeletons of our four northern Stylasterids. Examination by means of Mei gen's reaction has 

 shown, that the skeleton in all four is formed of aragonite. 



We here face one of the great problems of biology. There can be no doubt, that the power 

 of animals to produce aragonite in the one or the other manner must stand in connection with their 

 power to make use of the magnesium of the sea-water; according to the investigations of mineralogists 

 namely all aragonite contains magnesium. But what makes the matter so puzzling is, that alongside 

 the animals which have aragonite skeletons live some others, which like Corallium, Tubipora, Cysti- 

 phyllum and Anabacia form calcite skeletons. This shows that it cannot depend on a mere chance 

 whether the animal builds its skeleton of aragonite or calcite. It seems more than doubtful that 

 the crystalline system should be of any importance here. Physical characters might probably be 

 found in aragonite, which for most of the marine animals make it biologically more profitable than 

 calcite. Unfortunately the differences between aragonite and calcite in physical regards are still 

 so imperfectly known, that we are unable to form any reasonable supposition as to what part their 

 occurrence plays in the biology of the marine animals. 



