STUDIES IN SPICULE FORMATION. 157 
Fra. 3 (x 2600 diam.).—Adult microscleric holoxyhexaster. ‘Two nuclei 
have migrated from the central spherical mass of scleroplasm. 
Fra. 4 (x 1600 diam.).—Holoxyhexaster, about half-grown. 
Fie. 5 (xX 1250 diam.).—Adult microdiscohexaster, with several peri- 
pherally-situated nuclei (‘cells’). Each terminal is invested with a thin 
film of scléroplasm, though this is not always visible. 
Fia. 6 (x 2000 diam.).—Half-grown and adult forms of another variety of 
microdiscohexaster. 
Fic. 7 (xX 1600 diam.).—Central portion of an oxydiactine, showing the 
enveloping scleroplasm with distributed nuclei. The position of the four 
aborted rays is indicated by the mid-way swellings and axial cross. 
Fias. 8 (x 700 diam.), 9 (x 625 diam.).—Hexactines with the enve- 
loping scleroplasm well shown. 
MONACTINELLIDA. 
Fie. 10 (x 800 diam.).—Tylostyle of Microciona atrasanguinea in 
its scleroblast. 
Fie. 11 (x 1600 diam.). ge cea enolslostyle of M.atrasanguinea in its 
scleroblast. 
Fie. 12 (x 800 diam.).—Tylostyle of Suberites domuncula in its 
scleroblast. , 
Fie. 13 ee 1600 diam.).—Oxeote of Siphonochalina coriacea in its 
scleroblast. 
Fies. 14, 15 (x 1600 diam.).—Stylus and oxeote of Axinella poly- 
poides in their scleroblasts. 
Fies. 16, 17 (x 1600 diam.).—Acanthoxeote and spiraster of Cliona sp. 
in their scleroblasts. 
Fic. 18 (x 800 diam.).—Anisochela (one of a rosette) of Esperella 
lingua in its scleroblast. 
Fie. 19 (x 800 diam.).—Portion of tylostyle of E. lingua showing two of 
the several nuclei present in the syncytium enveloping the spicule. 
Fic. 20.—Development of the chiaster and spheraster of Tethya lyn- 
curium. a@ande represent the first appearance of the spicule as a siliceous 
globule. The rays appear on the surface of these globules much earlier in 
some cases than in others; ef. e.g. figs. d and e. As stated in the text, it is 
impossible to distinguish between the very young stages of the chiaster and 
the spheraster. A comparison of fig. g with figs. 4 andy shows well, on the 
other hand, that it is quite easy to distinguish adult chiasters from young 
spherasters of the same size. 
VoL. 52, PART 1.—NEW SERIES. 2 
