K. OKINOSEANA. — YOUXO SPECIMENS. 239 



Eespecting tlie spiculation of the siievc-plafe, I liavo to notice 

 the following : 



The main support of the beams is afforded by spicular 

 bundles whose cora2")onents are essentially the same as in the 

 pai'enchymal strands of tlie lateral wall. The only point of 

 difterence seems to consist in the fact tliat many of the diactins 

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

 1)6 called compass-needle-like, with or without knobs ;it the 

 middle. In extreme eases they are so short as to be only 250 /' 

 long, with a breadth of about 2") /< near the middle. Bpinose 

 microxyhexactins occur but rarely. Floricomes and oxyasters 

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

 are common. 



The dermal hexiictins, which occur very closely crowded 

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

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

 80-1^)0 // in length and 1-3-27 ,"■ in thickness at their base. All 

 the six rays in the spicule ai-e nearly equal in length and in gene- 

 ral appearance. They are generally tapering, minutely tubercled 

 on tlie outer part, and end either rounded or in a point. 



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 uupaired ray 

 of the pentactins dips into the parenchymal bundle. The said 

 spicules are j^i'csent 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 



