84 ART. 7. — I. IJIMA : HEXACTINELLIDA, IV. 



Spiculation. 



The jtarenchymal'm do not contain hexactins but consist ex- 

 clusively of diactins, as in C. meyeri rugosa. The diactins are 

 for the most part thin and small, terminating with i-ough swollen 

 ends; generally under l.ö mm. in length and 10 jx in thickness. 

 Occasionally there occur larger diactins which may be called the 

 principalia. These may attain a length of 3 mm. and a breadth 

 of 5b II at the middle. They are bow-like or ahnot?t straight 

 and differ from the smaller parenchymalia in tapering towards 

 both ends. On account of the general smallness and fineness of 

 the parenchymalia (PI. VI., fig. 8) the consistency of the sponge - 

 body is soft and delicate, as ascertained on spirit specimens. 



The firm stalk, on the other hand, contains parenchymal 

 diactins wdiich may be 10 mm. or more long with a thickness 

 of nearly 80 ij.. In its lower portion is observed the usual 

 synapticular coalescence between the principal supporting spicules. 

 The beams of the rigid framework are nearly smooth all over, 

 the microtubercles being present at places only in a sparse num- 

 ber, much as I have seen them in 0. pachyactina. 



The hypodermalia are mainly pentactins, which are supple- 

 mented by occasional diactins. The pentactins are small to 

 medium sized, the rays measuring up to 500 //. in length and 

 83 [J. \n Ijreadth at base. The unpaired proximal ray is some- 

 what longer than any of the paratangentials in the same spicule. 

 Each ray gradually tapers towards the roughened, usually coni- 

 cally pointed end. The above pentactins exist rather copiously^ 

 the spicular centers l)eing separated -from one another by an 

 interval which is a])proximately equal to the length of the para- 



