ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
295 
ventral origin of tlie genital pleura, the diffuse gonads, and the free 
pharynx. 
In the fact of the gill-slits being open directly to the exterior 
throughout their entire length, P. flava is more closely related to P. 
bahamensis than to any other described species. This is also indicated 
by the simple rows of paired liver saccules, as opposed to the irregular 
multiple arrangement in P. erythrsea. 
The genus or sub-genus probably represents an archaic type, as 
shown by the diffuse gonads, the free pharynx, and its littoral habitat. 
“ The gill-slits, branchial skeleton, and the temporary atrium formed 
by the apposition of the genital pleura in Ptychodera , offer a general 
homology to tho corresponding structures in AmpJiioxus and the 
Ascidians.” The differences are in many ways unimportant, and ‘‘such 
as might well be expected to occur in distinctly related forms with such 
totally different habits of existence, while others are to be accounted for 
by a wide interpretation of the principle of correlation between structure 
and function.” 
In an additional note Dr. Willey suggests that, until the form 
(Eschscholtz’s) is really re-found in the Marshall Islands, his own find 
might be called P. flava-cciledoniensis , or simply P. caledoniensis. 
Ctenoplana.* — Dr. A. Willey discovered a distinct new species of 
Ctenoplana (P. rosacea) in the Eastern Archipelago of British New 
Guinea. It will be remembered that this remarkable genus, which 
presents affinities both to the Ctenophora and to the Turbellaria, was 
established by Korotneff in 1886. This is now the second record of 
its occurrence. Dr. Willey describes the expert crawling and swimming 
movements ; the pinnate seizing tentacles, retractile within sheaths, 
perhaps belonging to the same category of structures as the proboscis 
of Nemertines and some Bkabdocoele Planarians ; the double character 
of the circlet of sensory tentacles surrounding the otolith, the testes 
and genital ducts, &c. He maintains that the tentacle axis of Cteno- 
plana corresponds to the longitudinal axis of Planarians, the stomachal 
axis of the former to the transverse axis of the latter, and the main 
axis of the former to the dorso-ventral axis of the latter. The solid 
pinnate tentacles of Ctenoplana are not bilateral, but biradial ; the 
ctenophoral plates, gastric lobes, gonads, gonaducts, and aboral sensory 
tentacles, are paired about the tentacle axis. The aboral sensory ten- 
tacles are homologous with the polar plates ( Polplatten ) of Ctenophora, 
and with the nuchal tentacles of Polyclades. 
Willey proposes to erect a new order Archiplanoidea for the recep- 
tion of Cceloplana and Ctenoplana ; and he suggests a hypothesis as 
to the diphyletic origin of Bilateralia which may be thus summarised : — 
o 
r Archiplanoidea 
k Cerianthidae 
f Ctenophora 
( Plathelminthes 
{ Anthozoa 
Coelomata 
* Quart. Journ. Micr, Sci., xxxix. (1897) pp. 323-42 (1 pi.). 
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