K. OKiyOSEAXA. — SOFT PARTS. 



247 



tius are soon added, at about a period when the parietal 

 oscula have begun to break through. Henceforth the derma- 

 lia that newly arise seem to be all hexactins ; so that these 

 soon greatly outnumber the original pentaetins. The earliest 

 formed hexaster is the graphiocome, the rhaphidial sheaves 

 derived from it being common at the stage when the der- 

 nialia consist as yet exclusively of pentaetins. The formation 

 of microxyhexactins, of the floricome, the oxyhexaster and 

 the oxystauraster soon follows. 



Soft Parts. 



The trabecuhr (PI. VIIT, fig. 30) are abundantly developed 

 in irregular cobweb-like ari:angement. They are thin and 

 filamentous, but here and there spread out into small film-like 

 areas. The protoplasm is granular, moderately stained by borax- 

 carmine. Nuclei belonging to it about ^^jnH in diameter, contain- 

 ing a group of chromatin grains. 



Dermal membrane with meshes or pores of irregularly angular 

 shape and of various sizes. INIeshes separated from one another by 

 thread-like, band-like or membrane-like trabeculse. It is more or 

 less extensively and continuously membranous towards, and on, 

 the tent-like conuli produced by the distal rays of the dermalia. 



Arclucocytes generally about 3 a in diameter ; found forming 



periphery of the larvae are stauractins, which in the adults are replaced by pentactin-der- 

 malla.— Probably the change in the dermalia, wliich \ have endeavored to demonstrate in 

 the young of R. okinoseana, is not peculiar to that species alone but is possibly common to a 

 wide circle of forms lielonging to the same family. I call attention to the stalked, evidently 

 very young Hexactinellid figured by F. E. ScnuLZE in the Chall. Eep., pi. xlii, figs. 5& G, 

 and referred to by him as tlie ' undetermined Crateromorphid.' The essential agreement in 

 spiculation between it and tlie little R. ohinmeana I liave described on p. 240 (su6 1.) makes 

 me believe that it is more probably a young Euplectellid, tlie pentactiu-dermalia of wliich 

 assumably give place to hexactins in a later period of life. 



