Interzoceeial Communication in Flustridee. By A. W. Waters, 285 
characters and the connection with the stolon will be found useful, 
but also the position of the diaphragms in the Ctenostomata furnish 
specific indications, and it is a matter of surprise that they have been 
so seldom mentioned in descriptions. 
In the Cyclostomata the connection is through very small pores, 
but their position and size I have sometimes used in determination. 
The connection is not always so simple as in Flustra, for often 
where at first sight we should imagine that the connection to a 
zocecium, either from its neighbour, from a stolon, or from a radicle, 
takes place directly, sections prove that there is an intermediate 
chamber, and that communication is thus made indirectly by the 
parenchym threads which enter and leave the chamber through discs 
or rosette plates. Hippothoa divaricata may be taken as a simple 
example of this, and also in Chorizopora Brongniartii Aud., and 
some species of Membranipora, there are chambers between the 
zooecia. In Porella cervicornis the distal rosette plates are in short 
tubes, while in Tubucellaria and some Celleporee the tube is of con- 
siderable length, often as long as a zooecium. 
The rosette plates have already been studied in Membranipora 
pilosa, and are referred to, and figured by Levinsen, in his ‘ Mosdyr * 
( £ Danske Dyr ’), but as a special form of rosette plate which has been 
overlooked can be more easily studied in this species than in Flustra y 
I give figures (plate VIII. figs. 1-i). There are two distal rosette 
plates, and usually four lateral ones, and the discs in this, as in so 
many other species, have a small “ watch-glass ” protection to them. 
In the upper part of the zooecium the discs are usually on the inside, 
but there is a certain amount of irregularity in this particular. (See 
plate VIII. fig. 1, and also fig. 12.) In the regular course of growth a 
new zooecium is added at the end of the parent ; but where a zooecium 
is intercalated, a large rosette plate two or three times the size of an 
ordinary one (plate VIII. figs. 3, 4) is formed on the inside of the old 
zooecium, and through this the connection is made to the additional 
zooecium. The growth in Flustra papyrea and several other Flustrse 
is similar, whereas in F. ovoidea, where increase takes place, there are 
two zooecia growing from the distal end of the parent. In Bugula 
calathus and some other cases a similar gigantic rosette plate is formed 
at the beginning of a new branch, and probably they occur in a large 
number of species. 
There is an interesting point worth mentioning, for the three 
species having internal denticles — F. dentigera , F. denticulata, F, 
spinuligera — each have six distal plates, and a row of lateral plates in 
all three species at about equal distances apart ; for while there are 
more rosette plates in F, spinuligera , it is only because the zooecia 
are longer ; thus a natural group seems indicated by both the denticles 
and the rosette plates. How questions of doubtful identification may 
be elucidated by means of the rosette plates is shown under the 
description of F. tenella and F. papyrea. 
1896 
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