16 
Huxley on Lacinularia socialis. 
The curious analogy in form between the genus Sfej}ha-- 
noceros and the Polyzoa has, I believe, been the chief considera- 
tion which has led many naturalists, both in England and on 
the Continent, to arrange the Polyzoa and Rotifera together. 
This has been done in two ways, either by denying the affinity 
of the Rotifera with the Vermes, and so approximating them 
to the Polyzoa considered as organized on the molluscous type, 
or, as Leuckhart has done, by admitting the affinity of the 
Rotifera with the Vermes, but denying that of the Polyzoa 
with the Mollusca. 
I believe that there is a fundamental error in each case, 
namely, that of approximating the Polyzoa and the Rotifera 
at all. The resemblance between Sfephanoceros and a Poly- 
zoon is very superficial. No Polyzoon has the cilia on its 
tentacles arranged like those of Steplianoceros ; nor has any a 
similarly-armed gizzard : still less is there any trace of the 
water-vascular system which exists in all Rotifera. 
The relations between the Polyzoa and the Rotifera, then, 
are at the best mere analogies. 
On the other hand, the general agreement in structure be- 
tween the Rotifera and the Annuloida — under which term I 
include the Annelida, the Echinoderms, Trematoda, Tur- 
bellaria, and Nematoidea — is very striking, and such as to 
constitute an unquestionable affinity.* 
The terms of resemblance are these : — 
1. Bands of cilia, resembling and performing the functions 
of the wheel-organs, are found in Annelid, Echinoderm, and 
Trematode larv2e. 
2. A water-vascular system, essentially similar to that of the 
Rotifera, is found in Monoecious Annelids, in Trematoda, in 
Turhellaria, in Echinoderms, and perhaps in the Nema- 
toidea.t 
3. A similar condition of the nervous system is found in 
Turhellaria. 
4. A somewhat similarly armed gizzard is found in the 
Nemertidae ; and the pharyngeal armature of a Nereid larva 
may well be compared with that of Alhertia. 
5. The intestine undergoes corresponding flexures in the 
Echinoderm larvae. There are, therefore, no points of their 
organization in which the Rotifera differ from the Annuloida ; 
* M. Milne Edwards, with his accustomed acuteness, pointed out 
(Annales des Sciences, 1845) the close afSnity of the Rotifera with the 
Annelids, the Turhellaria, and the Nematoidea ; but he did not include 
the Echinoderms in the group, doubtless because, at the time he wrote, 
sufficient was not known of the Echinoderm larva3 to demonstrate their 
truly annuloid nature. 
t To these may be added the Cestoidea and the Nemertidse. 
