324 
SIDNEY F. HARMER. 
permanently at a grade hardly higher than that of this 
hypothetical ancestor. Loxosoma shows itself the most 
primitive genus by the fact that it forms no colonies, by the 
greater development of the brain in the larva, and by the 
invariable presence of a foot-gland in the buds, if not in the 
adult. Rhab do pleu’ra and Cephalodiscus on the one hand, 
and the Ectoprocta on the other, have probably branched 
olf independently from the Entoproctan stem. In certain 
features the Gymnolsemata show themselves more archaic 
than the Phylactolsemata; this is perhaps the case with 
the “ body cavity,” whilst embryology, as far as we under- 
stand the facts, seems certainly in favour of this hypothesis. 
The occurrence of statoblasts, as well as the great differentia- 
tion of the funiculus, again prove that the Phylactolsem at a 
are in some of their characters at least as much modified as 
the Gymnolsemata. In the structure of the nervous system, 
the former are, however, perhaps more archaic than the latter; 
in Alcyonella, Nitsche (4) describes a large sub oesophageal 
ganglion sending off nerves to the lophophore, and connected 
in front of the (Esophagus by a thin commissure containing, 
however, no ganglion cells. 
The similarity in many important features between Loxo- 
soma and a Molluscan larva has already been pointed out, 
and of all organisms with whose ontogeny we are acquainted, 
the Mollusca come nearest to the Polyzoa. The com- 
parison between the development of the brain and pedal 
ganglia in Dentalium and the Hyaleacea, and the same 
structures in Loxosoma, may again be called attention to. 
The ciliated ring of the Entoprocta is very probably the 
velum, and the foot-gland the shell-gland. Allman’s sug- 
gestion that the buccal shield of Rhabdopleura (and hence 
the epistome of Loxosoma) may represent the mantle area 
of Lamellibranchs cannot be accepted, if we are to identify 
the dorsal organ as the brain. If it is necessary to look for a 
mantle cavity in the Entoprocta, it seems to me that we 
may possibly find it in the vestibule. In this case the tentacles 
would represent, not gill filaments of Lamellibranchs, but 
