558 Miss I. Sollas on Haddonella Topsenti. 
The general anatomy of the skeleton is shown in Pl. 
XXVIII. fig. 2; it consists of a number of separate fibres 
arising either singly or two or three together, from each disk 
of attachment. ‘The fibres branch at intervals, the ultimate 
twigs either terminating within conuli or expanding, at the 
tip, into disks of attachment similar to those found at the 
proximal ends of the fibres. The minute structure of the 
fibres recalls that of Janthella-fibres, for cells are present 
within their outer layers. 
The diameter of the fibres in their oldest portions, near the 
base, is 0°72 mm.; commonly in the upper parts they 
measured 0'4 mm. in diameter. 
As the genus Janthella is the only sponge hitherto known 
to contain cells in the cortex of its fibres, I may here recall 
the more striking of the other characters common to all its 
known species. ‘These are: the arrangement of the fibres 
into a regular square-meshed framework, horizontal fibres 
crossing others which rise vertically from a single basal disk, 
and secondly the restriction of oscula and ostia respectively 
to opposite sides of the plate-like sponge. Evidently the 
sponge now described cannot be included under the generic 
name Janthella; I therefore propose to call it Haddonella 
Topsenti. -Naturally up to the present Janthella has afforded 
the only available material for studying the development of 
pithed sponge-fibres with cell-containing cortex. The first 
worker to give an account of the minute structure of the 
fibres and to discover the cells contained therein was 
Flemming (6) in 1872. The species he examined were 
I. basta and I. flabelliformis. He describes the fibres in each 
of these as consisting of a rose-red finely granular pith, sur- 
rounded by an amber-coloured cortex in which are embedded 
beautifully contrasting violet-red cells. The pith showed a 
lumen of small dimensions which was not a continuous canal, 
but occurred chiefly at the points where the fibres branch. 
The “ Dornen”’ (small branches arising from the main fibres 
where these cross one another) were constantly free from cells 
at their apices. Flemming does not consider the question of 
the origin of the fibres or of their parts, but he goes only 
so far as to ask whether the cortical cells are proper to the 
sponge, or whether they are parasites, and decides that they 
are proper. In discussing the problem how, if they were 
parasitic, they could have got in, he mentions casually that 
the pith is naked at the apices of the “ Dornen.” He con- 
siders that the presence of cells in its fibres places the sponge 
in a very isolated position. “2 
Carter (7) gives a general account of the skeletons of horny 
