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 marojnal 

 thickening (Kaudwulst), has been compared by Kraepelin 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. air. Surrounding the atrial opening 

 is a fold in the ectoderm, and between the layers of this fold is a thin, 

 non-staiuable 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 homogeneous membrane in the fold, one can distinguish still 

 more highly refractive bodies, sjjht. 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 

 jSTitsche, 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 : " II se compose de plusieurs loges ou cellules placees bout a 

 bout ... en sorte qu'il n'y a aucune communication entre les differents 

 aniraaux." 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 mass, and therefore " dass wir in deni ganzen Apparat eine Vor- 

 richtung zu erblicken haben, durch welche Nahrstofflosungen des einen 

 Tieres mittels siebartig wirkender Cautelen in die Korperhohle des 

 Nachbarindividuums iibergefiihrt wei'den." 



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 



