(18) 



passes through thin stratca of celluloid, it might be expected that 

 the very thin layer of celluloid used in the above manner would 

 be no obstacle for the acid to attain the spicules. Even the retaining 

 of the reaction in this way is an advantage, as it may now be 

 observed without the use of very dilute sokitions. 



In this way we have constructed a little apparatus which has 

 answered to our purposes in several respects, viz : absence of glass, 

 slow reaction, rather great security for the lenses of the microscope, 

 and the possibility of interrupting the reaction at any moment. 



As we found it unmaterial whether the spicules (obtained from 

 sponges preserved in alcohol) were isolated by means of artificial 

 gastric juice (after some dciys at 35^ C) or by boiling with liydi-o- 

 chloric acid, we preferred the latter method. Such spicules, having 

 been boiled with hydrochloric acid for some minutes, washed out 

 repeatedly with water, either with the aid of a centrifuge or not, 

 and dried afterwards at the ordinary temperature, are the objects 

 investigated by us, if another treatment "is not expressly mentioned. 

 Hy placing some spicules in a drop of water, and covering them 

 with the thin film of celluloid, one can first study under the 

 microscope whether they are normal in their aspect, uninjured etc. 

 Also, and Tethya is a proper object for this, which spicules are open, 

 which closed. Then we expose the preparation to the vapours of the 

 hydrofluoric acid. The commencement of the reaction is more or less 

 retarded, depending upon the concentration of the acid, the quantity 

 of water and the thickness of the film of celluloid ; but at any rate 

 the spicules begin to be dissolved after some 30 or 50 minutes. 



It is best to give attention to the fractures, as the reaction is here 

 to be seen at first. 



BüTSCHLi (1901) already remarked that the dissolution of the silica 

 may occur in different ways. We can confirm this observation for 

 the styli of Tethya. Observing what happens at the broken end of 

 a spiculum, the opal surrounding the axial tiiread is seen to be 

 hollowed out in the shape of a cone. The top of the cone is Aery 

 sharp, and l)ecomes still shari)er if the reaction proceeds. BUtschli 

 says (1. c. 258 — 259) : "Man konnte wegen diesei- so haufigen 

 Bildung einer trichterförmigen Auflösungshöhle an den Enden auf 

 die Yermuthung kommen, dass die Angreifbarkeit und Loslichkeit 

 der Schichte]! von aussen uacli iiiiie]i, gegen den x\clisenfaden suc- 

 cessive zunehme. Eine solche Annahme scheint jedoch zur Erklarung 

 der Erscheinung nicht noting, vielmehr dürfte sie sich schon daraus 

 hinreichcnd erlautein, dass die Elusssaure almiihlich in den geöff- 

 neten Achsenkanal eindringt und gleichzeitig audi in dem Masse 



