562 Miss I. Sollas on Haddonella Topsenti. 
Summary. 
(1) The new genus Haddonella has its nearest allies in the 
species of [anthella (Gray); these two genera share the pecu- 
liarity of having cells in the cortex of their pithed fibres. 
(2) The fibre-tips or growing points consist of naked pith 
alone, secreted by a many-layered cap of spongoblasts. 
(3) Spongoblasts apply themselves sparsely to the sides 
of this pith, pouring out upon it a layer of spongin; upon 
this layer again spongoblasts settle and repeat the process of 
spongin deposition, and so on repeatedly till ultimately the 
pith is included in many successive sheaths of spongin, in the 
intervals between which the spongoblasts lie. 
(4) The spongoblasts diminish in size and lose their 
granular contents in the process of forming the spongin 
layers. 
The presence of cells in the spongin of sponge-fibres is a 
character of subfamily or family value (Polejaeff). 
Literature consulted. 
(1) VosmAER.—Zeitschr. f. wiss. Zool. 1871. 
(2) PoLtEyanFr.— Challenger’ Reports, vol. xi. 1884. 
(3) Von LENDENFELD.—Monoeraph of Horny Sponges. 1889. 
(4) Mtncury.—Text-book of Zoology, edited by E. Ray Lankester. 
1902 
(s) Giese, Zool. Soc. p. 49 (1869). 
(6) FLemmine.—Verh. d. phys.-med. Gesell. Wurzburg, vol. ii. p. 1 
(1872). 
(7) CarTer.—Ann. & Mag. Nat. Hist. ser. 5, vol. viii. p. 111 (1881). 
(8) Von LenDENFELD.—Zeitschr. f. wiss. Zool. vol. liv. p. 275 (1892). 
EXPLANATION OF THE PLATES. 
All the figures refer to Haddonella Topsenti. 
Pirate XXVIII. 
Fig. 1. Entire specimen, natural size, attached to a piece of coral. 
Fig. 2. Some skeletal fibres, partly diagrammatic. 
Fig. 3. Piece of the dermal membrane with dermal ostia and perforations 
of the oscular membrane. 
Fig. 4. Younger parts and apex of a growing fibre zn sztu. 
Fig. 5. Extreme tip of a growing fibre with spongoblast cap. 
Fig. 6. Cells from outer layers of the cortex of a fibre. 
Fig. 7. Longitudinal section of a fibre near the apex. 
Fig. 8. One side of the longitudinal section of a fibre. 
‘“g. 9. Similar part of a section of an older fibre. 
PLATE XXIX. 
Fig. 10. Longitudinal section of an adhesive disk. 
Fig. 11. Longitudinal section of a young stage in the development of an 
adhesive disk. 
a., algal cells which formed part of the surface of support; a.d., disk 
