REPOET OE THE ANNELIDA. 
205 
again, of two fairly formed heads followed by a few segments occurring at the anterior 
end of Typosyllis variegata, Grube. The heads pass off obliquely from the body. 
From the foregoing remarks it will be observed that in no group of the Annelids is 
budding more conspicuous than in the Syllida), and it is therefore not surprising that the 
remarkably branched form should have occurred in the same family. It is unique in the 
multiplicity of its divisions, which are all connected together by the body-wall and 
alimentary tube, and to which the size of the sponge alone fixes a limit. This much 
branched body is evidently the parent-stock, from which the male and female buds are 
produced, the resulting embryos conveying the species to new sites in other sponges. 
It had been observed, even in the days of Aristotle, that worms dwelt in sponges, and 
the occurrence of such forms as the phosphorescent Eusyllis under Sponges and Ascidians 
fixed to stones is a frequent occurrence in the littoral region in Britain. Though not 
uncommon in the Hirudinea, ectoparasitism in the chsetopodous Annelids is rare, the 
chief examples being observed in Slylaria, Chcstog aster, and other Naides. In the marine 
forms, again, commensalism is common, many examples inhabiting the tubes of others, 
taking shelter under the mantle of moUusks, or in the ambulacral grooves of starfishes. 
Fritz Miiller found an Amphinomian in the respiratory cavity of Leyms anatifera ; and 
amongst other examples is Alciopina parasitica, which Claparede discovered in Pleuro- 
hrachia densa. In Euplectella one of the Polynoidse occurs, and in an Ascidian another 
of the same fa mil y. Thus the presence of Syllis ramosa as a commensalistic form in the 
sponge is not remarkable. It is the unique power of branching which is noteworthy. 
Exogone, (Ersted. 
Exogone heterosetosa, n. sp, (PI. XXXIII. figs. 15, 16 ; PI. XXIV a, fig. 11). 
Habitat. — Dredged at Station 144a (off Marion Island), December 26, 1873; 
lat. 46° 48' S., long. 37° 49' 30" E. ; depth, 69 fathoms ; surface temperature, 41°‘0 ; 
sea-bottom, volcanic sand. It was found amongst the bristles of Lagisca antarctica 
during the examination of that form. 
A minute species, about 3 mm. in length and a third of a mm. in breadth. 
The body consists of thirty-four segments, which have a greater transverse than 
antero-posterior diameter, the latter attaining its greatest proportion posteriorly. The 
tail has a pair of cirri of considerable length. 
' The head (PL XXXIII. fig, 15) has anteriorly a pair of bluntly conical frontal lobes, 
which have a thin bridge along the middle line. A pair of eyes occur on each side, the 
axis of the pairs being directed forward and outward. The anterior on each side is the 
larger, and has a conical “ lens.” A short lateral cirrus is placed on each side of the head 
anteriorly, and there seems to be a median of similar length, though the^tate of the 
