32 BULLETIN OF THE 
but at its inner end fuses with the surrounding cylinder of cuticula. This 
inner cylinder, which is probably formed, as Kraepelin (87, p. 40) sug- 
gested, by splitting of the delicate cuticula at the base of the marginal 
thickening (Randwulst), has been compared by Kraepeliti to the “ collare 
setosum ” of Ctenostomes. The Randwulst itself I believe to be the equiv- 
alent of the Diaphragma of Nitsche, as I shall try to show later. 
At the deep end of the neck (Fig. 45), the inner layer of the bud is 
seen to be continuous with the ectoderm, The region of transition may 
be called the atrial opening, of. atr. Surrounding the atrial opening 
is a fold in the ectoderm, and between the layers of this fold is a thin, 
non-stainable homogeneous layer, slightly more refractive than the sur- 
rounding protoplasm. This membrane extends also a short way into 
the kamptoderm, and here lies between its two cell layers. Embedded 
in this homogencous membrane in the fold, one can distinguish still 
more highly refractive bodies, spht. On account of their form and 
high refractivity, I believe these to be muscle fibres cut across. The 
homogeneous membrane has also the same general appearance and 
relation to the muscularis as the so-called supporting membrane of 
Nitsche, and it is the only representative of that structure that I 
have found in Paludicella. 
9, DEVELOPMENT OF THE COMMUNICATION PLATE. 
In their description of Paludicella, Dumortier et van Beneden (’50, 
p. 40) say : “Il se compose de plusieurs loges ou cellules placées bout a 
bout . . . en sorte qw’il n’y a aucune communication entre les differents 
animaux.” Also Allman (56, pp. 114, 115) refers to the presence of a 
perfectly formed septum separating the cavities of adjacent “ cells.” To 
Kraepelin (87, p. 38) belongs the credit of having first carefully studied 
this structure in the adult by means of sections. He came to the con- 
clusion from the appearances which he figures (cf. my Plate V. Fig. 49), 
that there are small canals passing through the nearly homogeneous 
central mags, and therefore “dass wir in dem ganzen Apparat eine Vor- 
richtung zu erblicken haben, durch welche Nährstofllösungen des einen 
Tieres mittels siebartig wirkender Cautclen in die Körperhöhle des 
Nachbarindividuums übergeführt werden.” 
The descriptions of Kraepelin concerning the structure of the “ Roset- 
tenplate” are confirmed by my own observations, and seem to justify his 
conclusions concerning its function, The development of the organ has 
not, however, been carefully observed heretofore. Korotneff (74, Plate 
XII. Figs. 1 and 2) gives figures to show this process, but I have never 
