JOUKNAL aAmar. 



OF THE 



EOYAL MIOROSOOPIOAL SOCIETY. 



AUGUST 1881. 



TEANSACTIONS OF THE SOCIETY. 



IX. — On some Remarhable Enlargements of the Axial Canals of 

 Sponge Spicules and their Causes. By Professor P. Maetim 

 Duncan, M.B., F.K.S., Pres. Pi.M.S., Professor of Geology and 

 Mineralogy in King's College, London. 



(Read 9th June, 1881.) 



Plates VII. and VIII. 



It is well known that the spicules of siliceous Spongida may or may 

 not contain narrow axial tubular canals, visible under moderately 

 high powers of the Microscope. 



In many instances the canal resembles the capillary tube 

 of a thermometer in shape ; and it may be rounded, pointed, or 



EXPLANATION OF PLATES VII. AND VIII. 



Fig. 1. — An acuate, basally rectangulated spicule, with enlargements and 

 perforations. 

 „ la. — Another, enlargements great, penetrations. 

 „ 2. — Acuate, verticillately spined, open at the end, and with several 



enlargements. 

 „ 2a. — With one enlargement. 

 „ 26. — „ „ differing in shape. 



„ 3. — Cylindrical, entirely spined, with two perforations, a short normal 



canal, and a conoid enlargement. 

 „ 4a. — Spinulates, one is normal, the others have enlargements more or 



less irregular, of the axial and bulb canal. 

 „ 46. — Spinulate attenuate with axial canal, large in bulb, and rotten 

 looking at end. 



^^ „ 4c. — Curved spinulate with great bulbous enlargement and one near the 



''"^ open axial canal at the end. 



^ ,, id. — Penetrations in a piece of a spinulate. 



^1 „ 4e. — Spinulate with perforations and rugged axial canal-sides. 



^* „ 5a. — Attenuate acuate bent, enlargements simple. 



^ „ 56. — Greatly enlarged canals. 



.^ „ 5c.— Open axial canals and enlargements. 



P^ „ 5d. — Bulb and stem, ragged enlargements. 



„ 5e. — Thinning, fracture, and gradual narrowing of the axial tube to 

 where it becomes open. [Fig. 5/. 



Ser. 2.— Vol. I. 2 P 



CO 



