ON A LARVAL ACTINIAN PARASITIC IN A RHIZOSTOME. 227 
opening (Hacldon (8) ), and when the anemone is attached, 
would, I take it, function as does the conchula of P. hilli. 
McIntosh (9), writing of the parasitic larva of P. hastata, 
says : 
“ They appear to adhere to the medusa by the sucker- 
like action of the mouth, which is widely open, though 
the tentacles are closely applied to the surface. The 
free-swimming larval forms are thus, at a subsequent 
stage, carried about, without effort, by the medusae, and 
as there is abundance of nourishment of a suitable kind 
around, it is not necessary to limit the view only to the 
possibility of their feeding on Thaumantias, for by 
the use of their tentacles as organs of attachment the 
mouth may, at any time, bes et free.” 
My observations show that the larva of P. hilli adheres 
h>y the sucker-like action of the closely-applied oesophageal 
folds — the closed lips of the siphonoglyph completing the 
sucker — and that the tentacles are not brought into use. 
The larva is always found adhering in this way, save when 
escaping from its host, and it is through the conchula that 
the food is taken in. 
I am tempted to put forward the hypothesis that the 
larvae of the widespread genus Pea chi a are all meduso- 
philous, and that the single deep siphonoglyph, possessing 
as it does an opening below the oesophageal folds, is a larval 
organ, correlated with such parasitism. The development of 
a conchula, as a series of processes round the external open- 
ing, is seen in the older larvae. 
In support of this hypothesis I would draw attention to 
the distribution of the larval forms — of Peachia hilli para- 
sitic in Crambessa mosaica on the east coast op Aus- 
tralia; of Peachia parasitica on Cyanea arctica in 
the North Atlantic; of Peachia hastata on various 
medusae in the North Sea; and of Bicidium aequoreae, 
the probable larval form of P. quinquecapitata, off the 
-coast of British Columbia. 
In regard to the second and third forms, McMurrich (2) 
VOL. 62, PART 2. NEW SERIES. ] 6 
