HOLASCELLA TARAXACUM. 33 



The comital rhabds (Plate 22, figs. 29-36, 38-41) are diactines with a dis- 

 tinct thickening Ijong more or less centrally. They are 5-15 mm. long and the 

 two developed rays are, at their proximal end, near the centre of the spicule, 11- 

 45 II thick. They taper distally and measure, at their thinnest point, which is 

 usually situated a short distance from the end, 6-20 ^ in transverse diameter. 

 The end itself is usually thickened, more rarely conic and pointed. 



The two ends of the same spicule usuallj^ differ considerably from each other. 

 The terminal tliickening is oval or club-shaped and 20-47 fj. in diameter (Plate 22, 

 fig. 38-40). The ends of these spicules are sUghtly spiny, all the other parts 

 smooth. 



The more or less centrally situated tyle consists of four rudimentary rays, 

 the axial threads of which can always be distinguished as an axial cross within 

 it. The degree of reduction of these four rays is subject to considerable varia- 

 tion, and not infrequently the four rudimentary rays of the same spicule are 

 reduced to a very different degree. A series of forms representing different 

 degrees of ray-reduction is reproduced (Plate 22, figs. 29-35). 



The tri-, pent-, and hexactine comitals are rather rare. The triactine forms 

 are similar to the diactines above described and differ from them only by being 

 smaller and by one of their four reduced rays being much longer than the others. 

 The rays of these spicules are 17-25 m thick and the longest is 1.5-2.6 mm. long. 

 The pentactines and hexactines have rays 1-2.5 mm. long and 13-20 fj. thick. 



The long slender rhabds are centrotyle and similar to the diactine comitals 

 above described, so that one might consider them as giant forms of these. They 

 attain a length of 36 mm. and a thickness of 27 /i. The central tyle has a maxi- 

 mum thickness of 44 /u. Some of them have a very large terminal tyle, sometimes 

 70 ju in diameter, at one end. Rays thus terminally greatly thickened are cor- 

 respondingly reduced in length. The axial cross, which lies in the central thick- 

 ening, is in some of these spicules very irregular, the axial thread-rudiments 

 composing it enclosing angles very different from 90° with the axis of the two 

 developed rays. 



The rare minute rhabds, which may perhaps be comitals of the distal ray of 

 the hypodermal hexactines, but which were never seen in situ in this position, 

 are about 260 ^u long and 1.5 mm. thick. 



The proximal and lateral rays of the hypodermal and hypogastral hexactines 

 (Plate 22, figs. 1-4, 12-17) are 5-11 n thick at the base, cylindrical or only 

 slightly attenuated towards the end, and abruptly pointed or blunt. The proxi- 

 mal ray is 0.8-1.8 mm. long, tKe lateral rays are 0.2-1 nmi. The distal ray is 

 160-500 /u long, at the base 5-18 /i thick, and thickened more or less above. At 



