356 CUMINGS AND GALLOWAY MORPHOLOGY OP TREPOSTOMATA 



a new zooecium budded out of tlie distal region of the old one in the 

 usual manner. 



It is possible, following the suggestion of Levinseii, that the cysts are 

 due to the total regeneration of the zocecium; that we have here a zooe- 

 cium within a zorecium. There is not much, however, to support such a 

 view. It would be very difficult on such a supposition to account for the 

 appearances shown, for example, in figure 2. 



Another possibility is that the cystiphragms are due to a double-walled 

 arrangement analogous to the hypostega of some recent Chilostomata. 

 The overlapping character of the cystiphragms and their evident produc- 

 tion in succession, together with their sporadic occurrence in many spe- 

 cies, do not favor this interpretation. 



The cysts, with their inclosed brown masses, may be pathologic, due to 

 the entrance into the zooecium of deleterious foreign material or to para- 

 sitic bodies, and the consequent degeneration and death of the polypide. 

 This explanation would not be very different from the first explanation 

 given above. It Avould merely supply an exceptional rather than a nor- 

 mal cause for the degeneration of the polypide, and it would fit particu- 

 larly well those cases in which the occurrence of the cysts and brown 

 material is rare. It would hardly account for the regular occurrence of 

 such structures, for example, in Peronopora. In the experiments of 

 Harmer (13), mentioned above, the degeneration of a majority of the 

 polypides of a colony usually followed the introduction of the reagent 

 (Bismarck brown or indigo carmine) into the water in which the colonies 

 . were living. 



The occurrence of these cysts and their accompanying brown masses is 

 not confined to material from any particular locality or horizon. We 

 have found the structures in specimens from all portions of the Ordo- 

 vician, from the Chazy up, and from all of the principal provinces in 

 which these rocks are exposed. The structures are therefore not due to 

 any local conditions, nor are they peculiar to any special time. 



The cysts and brown masses are never found in the immature or axial 

 regions, nor even in the submature region of a zoarium. They are often 

 found in numbers just beneath an overgrowth. The indications are that 

 they are features of the fully mature portions of the zoarium. This adds 

 weight to the argument that they were produced in connection with de- 

 generating polypides. 



Communication Pores 



In his original description of Homotrypa curvata, Ulrich (29) men- 

 tions and figures "connecting foramina," passing through the inter- 



