Axial Canals of Sponge Spicules, dtc. By Prof. Duncan. 559 



Hexactinellids frequently present a minute spicule in their larger 

 spicules, or a canal may exist. 



AH the axial canals which have been described hitherto are 

 represented as extremely small tubes, which in some spinulate 

 spicula have a bulbous enlargement extremely narrow in its dimen- 

 sions. In some instances, general tubular enlargement of the canal 

 has been observed to occur, especially in young specimens, and 

 also as the result of internal decay.* 



On the occasion of the last Conversazione of this Society, on 

 April 20th, 1881, I had the pleasure of exhibiting several kinds of 

 sponge spicula which, with perfect external configuration, possessed 

 an internal series of elongate, conoidal swelHngs of the axial canal. 

 The variations in the size and number of these enlargements were 

 shown to be numerous, and they added greatly to the beauty of the 

 transparent siliceous spicula which contained them. A careful 

 examination of the subject has led me to bring it before you again, 

 as it possesses much interest to the microscopist, and relates to the 

 manner in which organic silica is dissolved in the deep sea. 



The specimens in one slide were given to me many months 

 since by Dr. Stolterfoth, of Chester, and they came from the 

 greatest known depth of the Pacific, in the neighbourhood of 

 Japan. Subsequently Dr. Stolterfoth kindly lent me six other 

 shdes from the same locality. 



Fig. 166.— Two cells on the spicule, occupying the position of circular concave 



depressions. 

 „ 16c. — A bulbous enlargement on a spinulate spicule. Distinct granules 



in a minutely granular matrix, faintly tinted green. 

 „ 16c?. — Granules greenish, arranged in separate masses in the end of a 



dilated axial canal. 

 „ 16e. — The upper view of b, closely resembling the zoospore of Achlya 



penetrans Dune. 



Measurements. 



-Length 3-00 ^^^ '■> breadth, greatest, tqVo incli. 



1 1 



55 200 " " 5' 12(»U '> 



1000 

 1 



1 100 



Diameter of penetration, -^-^ inch. 



* See infra, p. 566. 



2 p 2 



