VITKOLLULA FERTILIS. 43 



terminals, of which generally 4-7 are borne on each short princi- 

 pal. They are slender — at any rate not strong — and are distinct- 

 ly rough-surfaced. Though bent at the base, they are straight 

 for the rest of their length and so diverge from one another as 

 to give a spherical shape to the entire spicule. This measures 

 114-140 !>■ ; on an average 120 /v. in diameter. Cases of a 

 principal Ijearing less than three terminals probably never occur. 

 Certain it is that hemihexactinose and hexactinose oxyliexasters 

 a]"e both entirely foreign to the species. 



The only kind of discohexasters present is, as before indi- 

 cated, comparable to the microdiscohexaster of certain other 

 Rossellids. (PI. III., fig. 6). They measure only 26-30 r- in 

 diameter. The convex disc at the outer end of each tolerably 

 strong principal bears a bunch of numerous and exceedingly fine 

 divergent terminals, which end each in a minute terminal knol). 

 The shape of the entire rosette is spherical. In a certain speci- 

 men the discohexasters in question were met with only occasion- 

 ally ; in another they were quite common, especially near the 

 dermal and gastral surfaces, where they seemed to be somewhat 

 more numerous than the oxyhexasters. 



Soft Parts and Larvae. 



A glance at PI. III., figs. 8-11, will show at once that the 

 general arrangement of the soft parts is in essential agreement 

 with what we know of other Hexactinellids. 



The dermal mendjrane (fig. 10) is perforated l)y numerous 

 pores of various sizes ; its tissue separating these from one an- 

 other is at times quite thin and lilamentous, wdiile at other 

 times it is flat and film-like. 



