R. OKINOSEANA. — YOUXG SPECIMENS. 239 



Respecting the spiciilation of the sieve-plate, I have to notice 

 the following : 



The main support of tlie beams is afforded by spicular 

 bundles whose components are essentially the same as in the 

 parenchymal strands of the lateral wall. The only point of 

 difference seems to consist in the fact that many of the diactins 

 in the sieve-plate beam are of unusual shortness. These may 

 be called compass-needle-like, with or without knobs at the 

 middle. In extreme cases they are so short as to be only 250 ,« 

 long, with a breadth of about 25 />« near the middle. Spinose 

 microxyhexactins occur but rarely. Floricomes and oxyasters 

 have not been found, but the sheaves of graphiocome-terminals 

 are common. 



The dermal hexaetins, which occur very closely crowded 

 on the external side of sieve-plate beams, deserve special mention 

 (PL VIII, fig. 31). The rays are thick and short, measuring 

 80-lC)0 IJ- in length and 15-27 /^ in thickness at their base. All 

 the six rays in the spicule are nearly equal in length and in gene- 

 ral appearance. They are generally tapering, minutely tubercled 

 on the outer part, and end either rounded or in a j^oint. 



On the inside of the beams occur similar spicules which are 

 however mostly pentactins but occasionally stauractins, and which 

 are undoubtedly to be regarded as gastralia. The unpaired ray 

 of the pentactins dips into the parenchymal bundle. The said 

 spicules are present at wide intervals, so that the parenchymal 

 bundles are largely exposed to view^ on this side of the sieve- 

 plate. 



Young Specimens. 



The Science College collection contains an interesting series 



