Axial Canals of Sponge Spicules, &g. By Prof. Duncan. 561 



enlargements of the axial canal are not normal, and that they have 

 been superinduced upon a narrow and delicate tube structure. 



Several verticillately spined acuates, measuring -^Ijj inch in 

 length and T2V0 inch in extreme breadth, were examined. In one 

 type the spinules on the spicule are well developed and not very 

 close, the base is rounded and spined, and the shaft attenuates and 

 ends in a point. Several specimens have normal axial canals, and 

 two have them expanded. Thus in one (Fig. 2) the canal is 

 enlarged in the base, and increases in breadth for one-third of the 

 length of the spicule, and then it narrows suddenly with a rounded 

 contour into the normal dimension. It enlarges again, suddenly, 

 to about three times its usual diameter, and narrows slowly to 

 again expand and diminish before reaching the end of the spicule, 

 which is very slightly open. A second form, resembling that 

 just noticed in external configuration, but with less projecting 

 spinules, has the axial canal occupying two-thirds of the swollen 

 base and larger half of the spicule, and it then narrows to close to 

 the end, where it becomes open. Only one long and tapering 

 enlargement exists (Fig. 2a). Another type, with more numerous 

 and smaller spinules, has the axial canal enlarged as in the form 

 last mentioned (Fig. 2&). 



A sub-attenuate, cylindrical, entirely spined spicule ^ J-q- inch 

 long and ttV xr inch broad, has the axial canal slightly and equally 

 enlarged for about one-fourth of the length ; it then expands 

 rapidly with a rounded contour, and diminishes slightly, and forms 

 a large rounded canal in the rest of the spicule (Fig. 3). Other 

 spicula of the same form have only a very delicate, normal, tubular 

 axial canal. 



Cylindrical spicula very shghtly bent, with terminal inflations, 

 these last only spined. Such a spicule rhs iiich long and tAo inch 

 broad, has a perfectly plain cylindrical body, and in the centre, for a 

 small space, a normal axial canal ; but on either side, it enlarges 

 about five times, terminating in rounded ends in the extremities of 

 the spicule. These great expansions are filled with air in the 

 specimen (Figs. 9, 9a). 



In another specimen, basally spined but otherwise resembling 

 it, a great enlargement has been broken across, and there are two 

 smaller swellings with a short normal part (Fig. 9&). 



There are many whole and fragmentary spinulate and fusiformi- 

 spinulate spicula in the deposit, and many specimens are normal, 

 the axial canal being very delicate and normal, and the usual 

 globose enlargement in the head of the spicule is very small or 

 it may be linear. 



The departures from the normal type are numerous, and may 

 be treated under different heads. (1) Enlargement of the axial 

 canal, with opening at the small end of the spicule. In one 



