THE ANATOMY OF THE MADREPORARIA. 
589 
condition of the specimens, which did not allow of their being 
dissected out. 
The ova are developed on all three orders of mesenteries ; as 
their origin and position does not appear to differ from the 
type described by the brothers Hertwig for Actinia, no figures 
are given. I have not seen the testes, hence Flabellum may 
be regarded as dioecious. The filament is present along the 
whole course of the free edge of the mesentery, including that 
region in which ova are developed. The latter is mostly below 
the part which is characterised by great contortion of the free 
edge and by (?) the giving off of acontia. 
iii. Histology. — The ectoderm of the mouth-disc (fig. 6) 
is characterised by deeply- staining, very numerous nuclei; and 
has distinctly the appearance of a secreting layer. It probably 
produces a similar secretion to the slime poured forth in 
quantities by an irritated Actinia. 
This figure (which is a section along the line a, fig. 2) is 
taken from a well-grown polyp, and shows traces of the 
originally basal ectoderm which secretes the corallum (the 
calycoblasts of v. Heider) {ch., fig. 6). In a younger and 
actively growing polyp these are much more definitely marked 
( ch ., fig. 7). The nuclei lie in a gelatinous-looking matrix, 
which stains slightly with borax carmine, but in which no cell 
outlines are distinguishable. In the calycoblast layer sur- 
rounding the septum, at the same height and in the same 
polyp, the nuclei are much rarer {ch., fig. 8). 
The characters of the ectoderm alter considerably on the 
tentacles; as above mentioned, it is on them raised into 
a series of knobs, each of which is a “ battery ” of nemato- 
cysts. A transverse section through the wall of a tentacle is 
shown in fig. 9, and exhibits the structure of a battery ; the 
nematocysts are confined to the peripheral part, and behind 
them lie a very large number of nuclei, probably instrumental, 
as was first suggested by v. Heider, in the formation of the 
cells which replace the ejected nematocysts. On the peripheral 
face of the mesoderm-lamella lie longitudinal muscle-fibres 
