112 ART. 7. 1. IJIMA : HEXACTINELLTDA, lY. 



forms a sieve-like layer covering over the entrances into the ex- 

 current canals. 



Spi dilation. 



The parenchymalia are all slender diactins in loose felt-like 

 arrangement or grouped together into thin ill-defined bundles. 

 The principalia may attain a length of 17 nnn. or more and a 

 breadth of 100 u at the middle ; they taper gradually towards 

 botb the smooth and sharply pointed ends. There exist all sizes 

 down to coinitalia only 8 // in thickness. All the smaller diact- 

 ins have rough ends, which may be tapering l)ut are more usually 

 slightly swollen and terminating in a conical or rounded tip. In 

 all the j^arenchymalia the spicular center is externally evenly 

 contoured. 



The hypodermalia and hypogastralia are both likewise diact- 

 ins, generally 1Ä-20 fi in breadth and under 3^ mm. in length. 

 They quite agree in appearance with similarly sized parenchy- 

 malia, except in the fact that the spicular center is often, but 

 not always, externally marked by an inconspicuous annular swell- 

 üig. They are generally arranged into thin strands of varying 

 strength. The manner in which these strands make up the hypo- 

 dermal and hypogastral latticework has already been dwelt upon. 

 No pentactins enter into their composition. 



The dermalia (PI. YIII., fig. 20 ; PI. IX., fig. 12) are pre- 

 dominantly pentactins in which the ]dace of the atrophied sixth 

 ray is generally indicated V)y a gentle swelling on the distal side 

 of the piratangential cross. Exceptionally they are represented 

 by stauractinic forms, in which the two aborted rays in the radial 



