12 
Dr Hcirmer on the Structure and Glassification 
Waters describes the compensation-sac, without understanding 
its mode of action, in Galwellia sinclairii, G. bicornis, Urceolipora 
dentata, Onchoporella bombycina (?), and Iclithyaria oculata ( ?); 
his account 1 appearing in the same year as Jullien’s and quite 
independently of it. 
It is perhaps owing to Jullien’s remarkable views on the 
subject of Zoological nomenclature that his results have been 
either ignored or discredited by later observers. The existence of 
the compensation-sac is denied by Pergens 2 for species of Schizo- 
porella in which it is certainly present ; and Levinsen 3 expressly 
controverts the statement that the so-called “ median pore” of 
Microporella malusii is open to the exterior. 
I have been led to make observations on this subject as the 
result of the examination of what I believe to be a new species of 
Euthyris 4 , kindly sent to me from Port Jackson by Mr T. White- 
legge. The study of this species completely confirms the accuracy 
of Jullien’s statements. I am fully in accord with him in 
attaching importance to the characters of the “ front-wall,” or 
“ par oi frontale,” as a guide to the classification of the Cheilosto- 
mata. His statement that the compensation-sac occurs “ chez 
toutes les especes de Cheilostomiens monodermies 5 ” is a generali- 
sation which does not appear to have been founded on a large 
number of cases ; but it is nevertheless in all probability sub- 
stantially true. 
My own results may be summarised as follows : — 
(i) The central group of the Cheilostomata is constituted by 
such families as the Membraniporidae, Flustridae, Farciminariidae, 
etc. In these the front wall (= opercular wall) remains entirely or 
to a large extent membranous, the membranous part being known 
as the ‘‘aperture.” The operculum is a moveable part of this 
membrane, its base-line not being usually strengthened by a basal 
sclerite, the presence of which would introduce rigidity where 
flexibility is most wanted. A series of parietal muscles originates 
from the lateral wall of the zooecium, on each side, and is inserted 
into the membranous aperture. The contraction of these muscles 
exerts a pressure on the fluid of the body-cavity, and thereby 
causes the protrusion of the polypide; — a mechanism described 
by Nitsche in 1871 6 . 
(ii) A second group of Cheilostomata is constituted by the 
1 Challenger Reports, “ Polyzoa Suppl.” Part 79, 1888, pp. 17, 18, 3, 10. 
2 “ Untersuchungen an Seebryozoen,” Zool. Anz., xn. 1889, p. 507. 
3 “Polyzoa, Hauchs Togter,” Copenhagen, 1891, p. 285. 
4 I hope to publish an account of this species in a paper dealing more fully with 
the compensation-sac. 
6 Mem. Soc. Zool. France, i. 1888, p. 275. The “monodermies ” correspond for 
the most part with the Lepralioid or Escharine forms of other authors. 
6 Zeitschr. wiss. Zool., xxi. p. 426. 
