CALCAREOUS SKELETON OF THE ANTHOZOA. 515 



position of the Nicols ; these of course were due to the irregu- 

 larity of the crystalline fibres of which the cords are composed. I 

 have dwelt at some length on the structure of the inorganic part 

 of the spicule of Spongodes^ because I am able to show 

 that all its details are moulded, as it were, upon an organic 

 matrix. 



Kolliker, as has been stated above, denied the existence of 

 axial fibres in the spicules of Alcyonaria. Some fortunate 

 preparations of the partition walls of the stem canals in 

 Ammothea arborea and Siphonogorgia mirabilis re- 

 vealed the presence of an organic filament in the spicules of 

 the partition walls of these species. Following up this obser- 

 vation I was able to discover similar axial and also radial fibres 

 in the spicules of Spongodes, but not without considerable 

 trouble. Kolliker remarked that hydrochloric acid gave much 

 more uncertain effects than acetic. I found that treatment with 

 even very dilute solutions of hydrochloric or nitric acid removed 

 all traces of the axial organic basis. Decalcification with picric 

 or very weak picro-nitric acid had the same effect, but very 

 careful decalcification with a '5 per cent, solution of acetic acid 

 and subsequent staining with aqueous safrauin and picro- 

 nigrosin brought out the structure shown in fig. 12. The 

 spicules, which were removed with needles from the colony, 

 always had a certain amount of mesogloea adherent to them. 

 This was stained blue by the picro-nigrosin, and thus differen- 

 tiated from the spicular sheath, which was stained crimson by 

 the safranin. The sheath retained more or less faithfully the 

 shape of the spicule, and the warts or projections due to the 

 emergence of the radial cords on the surface were clearly 

 seen. I could detect no trace of fibrillar or other structure 

 in the uninjured sheath, though it broke up readily into 

 longitudinal fibrillae when torn or otherwise injured. Within 

 the spicule sheath is an arrangement of organic fibrillae, 

 represented as faithfully as possible in fig. 12. These 

 fibrillae are stained deep orange by safranin, and stand out 

 conspicuously from the spicule sheath. The axis of the 

 spicule is occupied by a dense feltvvork of longitudinal fibrillte. 



