4G 
Proceedings of the Royal Society 
Monday, Ibtli Becember 1862. 
Pkofessor CHEISTISON, V.P., in the Chair. 
The following Communications were read : — 
1. On the Eepresentative Eelationships of the Fixed and Free 
Tunicata, regarded as two sub-classes of equivalent value ; 
- with some general remarks on their morphology. By 
John Denis Macdonald, Esq., E.N., F.E.S., Surgeon H.M.S. 
“ Icarus.” Communicated by Professor Maclagan. 
In tliis paper the author maintains the proposition, that the 
class Tunicata may be conveniently divided into two sub-classes, 
viz., the Fixed or Stationary, and the Free or Locomotive, of at 
least nearly equal value in a zoological point of view, in opposition 
to the opinion commonly entertained, that the so-called Pelagic 
Tunicata compose a group only commensurate with the groups of 
the Compound, the Social and the Simple, into which the Fixed 
Tunicata have been divided by Milne-Edwards and others. 
After some general remarks on the morphology of the class 
’Tunicata, the author proposes the classification, of which the fol- 
lowing are the leading subdivisions, and under which he groups 
and classifies the various genera of Tunicata. 
Tunicata. 
Sub-class Isif . — Animals fixed or stationary. 
I. Branchial membrane closely adherent, or more or less per- 
fectly sac-like ; simply areolated or distinctly retiform, the 
meshes disposed in many transverse series without non-ciliated 
supporting bars. 
1. G-emmse springing directly from the parent, with a temporary 
bond of union — Simple Tunicata. 
2. Grommse springing separately from a definite “ ascidiarium ” 
(Hux.), and communicating indirectly through a central 
common vascular system — Social Tunicata. 
3. G-emmai arising separately from the parent with or without 
vascular intercommunication, but always immersed in a 
common test or “ascidiarium” — Compound Tunicata. 
