Huxley oii Lacinularia socialis. 
19 
their larval state, and hence 1 do not hesitate to draw the con- 
clusion (which at first sounds somewhat startling) that tlie 
Rotifer a are the 'permanent forms of Echinoderm larvae^ and 
hold the same relation to the Echinoderms that the Hjdriform 
Polypi hold to the Medusse, or that Appendicularia holds to 
the Ascidians. 
The larva of Sipunculus might be taken for one of the 
Rotifera ; that of Ophiura is essentially similar to Stephano- 
ceros ; that of Asterias resembles Lacinularia or Melicerta. 
The pre-trochal processes of the Asterid larva Brachiolaria are 
equivalent to those of Brachionus. 
Again, the larvae of some Asterid forms and of Comatula 
are as much articulated as any Rotifera. 
It must, I think, have struck all who have studied the Echi- 
noderms, that while their higher forms, such as Ecliiurus and 
Sipunculus^ tend clearly towards the Dioecious Annelida, the 
lower extremity of the series seemed to lead no-whither. 
Now, if the view I have propounded be correct, the Rotifera 
furnish this wanting link, and connect the Echinoderms with 
the Nemertidae and Nematoid worms. 
At the same time it helps to justify that breaking up of the 
class Radiata of Cuvier, which I have ventured to propose 
elsewhere, by showing that the Rotifera are not " radiate " 
animals, but present a modification of the Annulose type — 
belong, in fact, to what I have called the Annuloida, and 
form the lowest step of the Echinoderm division of that sub- 
kingdom. 
From our imperfect knowledge of the Nematoid worms it 
is difficult to form a definite scheme of the affinities of the 
Annuloida; but perhaps they may be sketched as in the 
Diagrams, pi. III. 
These diagrams represent the arrangement of the ciliated 
bands with relation to the axis of the body in the Rotifera. 
Underneath each Rotifer is an Annelid or Echinoderm larva, 
with its ciliary bands represented in a like diagrammatic 
manner, to show the essential correspondence between the two. 
This p^iper is now printed exactly as it was read before the Micro- 
scopical Society on the 31st of December, 1851, with the exception of 
those notes which refer to the very excellent memoir of Dr. Leydig, pub- 
lished in February, 1852. Dr. Leydig must have been working at the 
subject at about the same time as myself, in the autumn of last year ; 
and if I refer to the respective dates of our communications, it is merely 
for the purpose of giving the weight of independent observation to those 
points (and they are the most important) in which we agree. 
It is the more necessary to draw attention to this fact, since Professor 
Ehrenberg, in a late communication to the Berlin Academy, hints that 
the younger observers of the day are in a state of permanent conspiracy 
against his views. T H H 
Juhj 9, 1852. 
c 2 
