Axial Canals of Sponge Spicules, &e. By Prof. Duncan. 567 



be observed to occupy the inner extremities respectively, recalling 

 strongly to mind the appearance of the saprolegneous cell Pythium 

 when working its way through the cell-wall of Spirogyra. 

 KoUiker gives good figures of the first recorded form of this, 

 merely observing that it is a ' pecuhar degeneration.' " * 



Mr. Carter's figure of the penetrations from without, appended 

 to his essay, resembles those which I have seen to a certain extent, 

 but none of those in the spicula mentioned in this communication 

 end in globular swellings. My friend does not appear to have seen 

 them opening into the axial canal, nor has he seen the remarkable 

 series of enlargements of the axial canal now noticed. Certainly 

 they do not relate to young sponge spicula or the ground-work 

 spicula around which a mature one could develop. 



The cylindrical borings, for such they are, are found on all parts 

 of sponge spicula, and are very common. Very few of the spicula 

 of the deep-sea deposit now under consideration are without them. 

 The diameter of the tubes, which are invariably cylindrical, differs, 

 t-oVtj- inch being exceptionally large. Some are mere lines under 

 high powers, and in some spicula the first stage of the boring 

 process is well seen (Figs. 5, 6**, 6*). Moreover, concavities 

 occur in greater or less numbers, or they may be sohtary, on the 

 outside of the spicule : they are circular in outline, and are below 

 the level of the outside of the spicule. Others represent the 

 next stage, where boring has not quite reached the axial canal (Fig. 

 12&). The last stage, in which the axial canal has become very 

 slightly enlarged close to a perforation into it, is shown in Fig. 12a. 



Fig. 4:d is a part of a spicule showing three penetrations, 

 which reach far in towards the axial canal, five large ones which 

 reach the canal, and three which are seen from above and resemble 

 circular disks of light. Besides, there is at one extremity of the 

 piece, a ragged penetration which has evidently had to do with 

 the fracture. In this instance the axial canal is abnormally wide, 

 but has not its calibre irregularly enlarged. Fig. 10a is a view of 

 the end of a spicule with penetrations from without, and a gradually 

 enlarging canal. Fig. 1 1 is a view of a very curiously shaped spinu- 

 late, and the three borings are incomplete. Fig. 11a is of part of 

 the axial canal of another specimen, in which entrance of water from 

 without has been made possible. Fig. 12 is of the entrance of a 

 perforation into an axial canal on an acerate ; the canal is slightly 

 enlarged, and in one place is beginning to form a symmetrical 

 space. Under the Microscope the texture of the wall of the canal 

 is not clear, but that of the perforation is bright. Figs. 5 and 12a 

 show the progress of erosion of the axial canal. Fig. Vlh shows 

 incipient penetrations, one being oblique. Fig. 14 shows a multi- 

 plication of penetrations and enlargements on a long acuate. 

 * ' Icones Histologicse,' der feinere Ban, p. 83, pi. viii., fig. 10. 



