E. OKINOSEANA. — SOFT PAETS. 247 



tins 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 pentactins. 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 pentactins. The formation 

 of microxyhexactins, of the floricome, the oxy hexaster and 

 the oxystauraster soon follows. 



Soft Paets. 



The trabecukc (PI. VIII, fig. 30) are abundantly developed 

 in irregular cobweb-like arrangement. 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 27, ,« in diameter, contain- 

 ing a group of chromatin grains. 



Dermal membrane with meshes or pores of irregularly angular 

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

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

 less extensively and continuously membranous towards, and on, 

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



Archœocytes generally about 3 ji. in diameter ; found forming 



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

 malia. — Probably the change in tlie dermalia, which I have endeavored to demonstrate in 

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

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

 very young Hexactinellid figured by F. E. Schulze in the Chall. Eep., pi. XLii, figs. 5 & 6, 

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

 spiculation between it and the little R. okinoseana I have desciihod on p. 240 {mh 1.) makes 

 me believe that it is more probably a young Euplectellid, the pentactiu-dermalia of which 

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



