B. W. PRIEST ON SPICULES FROM THE OAMARU DEPOSIT. 255 



will almost always find the presence of an axial canal remaining 

 hollow in the silicious spicules, although in some few of the larger 

 , forms we occasionally meet with mere imperceptible lines, indica- 

 tions of where it had once been, while others are entirely filled 

 in with the material with which the spicule is composed. I might 

 just mention here that we invariably find the cavity in the calcareous 

 spicules quite obliterated. 



Now it is the axial cavity of the silicious spicule to which I wish 

 to draw your attention, as it is that with which we have to deal. 

 A great many of the spicules from Jackson's Paddock have the 

 appearance of being cracked all over in the same way that one 

 meets with in unannealed glass, which is no doubt due partly to 

 pressure and partly to heat in the deposit, occurring as it does in a 

 volcanic district, some sudden change of temperature acting in that 

 way upon them. Some will be found having a pitted appearance, 

 such as we see sometimes in old Roman glass, and others with the 

 peculiar enlargement of the axial cavity which we meet with in the 

 spicules found in the deposit from Port Jerenii Hayti and in some 

 of the deep sea soundings, which latter were made the subject of a 

 paper read before the Royal Microscopical Society in 1881 by 

 Professor Duncan. These enlargements, forming as they do such 

 a beautiful and regular pattern, are evidently, and now generally 

 acknowledged to be, due to the action of some penetrating organism 

 at some time or another, probably allied to the minute alga Palcea- 

 chlya perforans, as in the recent spicules so acted upon a green 

 colouring matter answering to the zoospores has been seen. 



Now in the present case I have come across two spicules, one an 

 acerate, the other a trifid, in which the enlarged axial cavities 

 have a spiral, vermiform-looking body lying within them, and 

 perfectly silicious, the silica being chalcedonic, and seems to have 

 derived its silica from that of the spicule itself. Now the question 

 to me arises whether this curious formation is due before fossiliza- 

 tion to the penetration of a minute organism, which, as it died, was 

 replaced by silica derived from the spicule, and thus causing the 

 cavity in which it lies, assisted by the action of sea water, which is 

 known to have a caustic action on dead sponges, or after deposition 

 of the spicule and subsequent fossilization an infiltration of silica 

 took place in the axial cavity, gradual disintegration of the spicule 

 occurred internally, the internal structure being, I believe, more 

 susceptible of decay than the external at first. 



