122 HENRY BURY. 
lobe, we are not at present in possession of any facts to show 
that the same part of the lobe is involved in both these cases; 
so that even the proof of the homology of their position is 
yet imperfect, while the proof that they had a common 
origin, and are therefore completely homologous, is further 
off still. 
We have seen that the organs connected with the preoral 
lobe of Echinoderm larve are situated in the radial stage, in 
what I have called the anterior interradius; and it is evident 
that a disc of fixation arising in this interradius might very 
easily appear, in ontogeny, to be a part of the preoral lobe 
itself. That some such confusion of two phylogenetically 
distinct structures does occur in the larva of Antedon is very 
strongly suggested by the fact, to which I have already drawn 
attention, that the so-called przoral lobe of this larva contains, 
at the time of fixation, certain structures (skeleton and con- 
tinuation of the right body-cavity) which cannot well be re- 
garded as primarily belonging to this lobe, but rather to the 
stalk, which is itself apparently a secondary structure—the 
earliest Pelmatozoa having been, as paleontology teaches, 
sessile. 
The position of the water-pore in the larva of Antedon also 
accords very well with the view here advanced, though it is 
not inexplicable on other hypotheses. It is difficult to illustrate 
this point without undue multiplication of diagrams, but 
perhaps fig. 50 may be of some service. I have assumed that 
the disc of fixation arose in the interradius of the anus and 
water-pore in such a stage as is shown in fig. 48, and then 
moved round to the aboral pole. If, before this movement 
had proceeded far, the stalk and the extension of the right 
body-cavity into it were, in ontogeny, precociously developed, 
something very like fig. 50 would be reached; compare this 
with the larva of Antedon at the moment of fixation, and we 
shall see a possible reason why the water-pore in this larva is 
so far removed from that dorsal position which it assumes in 
other Echinoderm larve. 
Of course I am well aware that the above suggestions as to 
