52 
SUMMARY OP CURRENT RESEARCHES RELATINO TO 
Terminal Polyp and Zooid in Pennatula and Pteroeides.* — Prof, 
G. v. Kocli gives figures of various stages of young and just adult 
specimens of Pennatula phosphorea. In the earlier stages it is quite 
easy to make out a terminal polyp, with a terminal pore or terminal 
zooid at its base. This arrangement is no longer apparent in an example 
with fourteen leaves, for the polyp is gone though the zooid is still 
terminal, and the same is the case in a specimen with thirty-eight 
pinnules. A short notice is also given of two young colonies of 
Pteroeides spinosus. 
Structure of Cerianthus americanus.f — Prof. J. Playfair M‘Murrich 
gives an account of the structure of Cerianthus americanus. The largest 
specimen obtained measured about 20 cm. in length, but those de- 
scribed by Verrill were much larger. The mesenteries are arranged on 
a very different plan to those of C. menibranaceus and C. borealis ; more 
than one pair reach the extremity of the body ; there are in all ninety- 
two mesenteries, twenty-three of which are well developed, or pass more 
than half-way down the column. The sexes are separate, and the three 
specimens examined by the author were all females. The examination 
of the histological structure showed many points of resemblance to 
C. membranaceus and of difference from C. borealis . The author gives 
a detailed account of what he was able to observe. The ova are large 
and are imbedded in the mesogloea of the mesenteries ; the nucleus is 
lc^rge and always excentric, and usually projects very noticeably beyond 
the general surface of the ovum ; one large nucleolus is always present. 
Organization of Monobrachium parasiticum.f — Herr J. Wagner 
has made a study of this fine Hydroid, discovered by Merejkowsky in 
1877. In most colonies the centre is almost entirely occupied by 
sexual individuals, while at the periphery the gonophores are intermixed 
with the hydranths, and at the extreme edge there are special forms, 
for which the author proposes the name of pseudonematophores. These 
last represent the “ spiral zooids ” described by Allman in Podocoryne, 
and by various authors in other forms. In Monobrachium the terminal 
swelling is a true battery of nematocysts, and the organ has clearly a 
defensive function. They differ from true nematophores by the pos- 
session of a prolongation of the gastric cavity, which is always wanting 
in true nematophores. Further, they do not emit pseudopodia, and in 
these two points the pseudonematophores approach the hydranths, 
between which and the nematophores they form an intermediate stage. 
Monobrachium is nourished on the excrements of Tellina , to the shell 
of which it is fixed; and, as the currents produced by the siphons 
continually bring fresh water, this Hydroid may be regarded as a com- 
mensal. On the other hand, the protractile and single tentacles may be 
of use to the Molluscs, and we may, therefore, have to do with a case of 
symbiosis. 
The ectoderm of the hydranths and of the pseudonematophores is 
formed by epithelio-muscular cells, every one of which seems to have the 
power of transforming itself into a supporting cell. The subepithelial 
* Morphol. Jalirb., xvi. (1890) pp. 396-8 (7 figs.), 
f Journal of Morphology, iv. (1890) pp. 131-50 (2 pis.), 
j Arch, de Biol., x. (1890) pp. 273-309 (2 pis.). 
