88 ALLMAN, ON APPENDICULARIA. 
the open convex edge or base outwards, and the remaining 
open edge backwards and inwards. 
The convex edge of each fan nearly reaches the surface of 
the gelatinous mass, to which it then runs almost parallel, 
extending forwards upon each side to within a short distance 
of the anterior extremity of the greater diameter, and back- 
wards to a point nearly opposite to the junction of the 
posterior and middle third of this diameter. 
The surface of each of the double fans is marked with 
numerous regular corrugations, apparently formed by folds 
of the membrane, which converge from the whole of the 
convex margin towards the apical angle where they gradually 
die out. 
Towards the convex margin the fans are colourless and 
transparent, but towards the apex they lose their transpa- 
rency and assume a light-yellow colour. 
About midway between the apices of the fans and the 
posterior extremity of the greater diameter, and in a vertical 
plane passing through this diameter, is situated the body of 
the Appendicularia. So far as I could make out it seems to 
be simply imbedded in the gelatinous mass, having its respi- 
ratory aperture directed towards the apex of the fans, while 
its tail alone is free, and by the constant vibrations of the 
latter the whole structure is carried about through the sur- 
rounding water. 
On each side of the spot in which the body of the Append- 
icularia 1s imbedded the gelatinous investment presents an 
elliptical superficial patch of a yellowish colour, to which 
there invariably adhered Naviculze and other minute bodies, 
Beyond the poits now described in this most curious 
appendage I have not succeeded in detecting any other 
structure ; no trace of the vascular network described by 
Mertens was observed, and we must assuredly deny the 
respiratory function ascribed to the appendage by its original 
discoverer. I must also add that I never witnessed its re- 
newal after destruction, which Mertens mentions as occurring 
within so short an interval as half an. hour. 
A comparison of the body described in the present com- 
munication with that noticed by Mertens will show that, 
besides the total absence of the vascular network, it differs 
considerably in detail from the corresponding appendage of 
the Behring’s Straits specimens. In these it is considerably 
larger than in the specimens from the Clyde, while Mertens 
describes and figures under the name of “ horns’ two pairs 
of folded laminz, represented in the present species by the 
single pair of fan-like structures; and the shape of these, in 
