172 E. R. Cumings — Development of Fenestella. 



The Primary Buds. 



Two lateral primary buds arise from the primary zooecium 

 (figs. 3-7, 21-23, 40-43). There is still some question as to 

 whether these buds arise from the protoecium or from the 

 ancestrula. The sections figured reveal all that can be ex- 

 pected. The question becomes one of interpretation and of 

 analogy with recent Bryozoa. The proximal ends of the pri- 

 mary buds are in contact with the protoecium and are separated 

 from its cavity by a very thin calcareous wall, which is fre- 

 quently broken away (figs. 19 and 20). The appearance of this 

 wall is well shown in figure 36. Figures 3-7 and 38-40, 42 

 show the intimate relation of the primary buds to the pro- 

 toecium. From the analogy of recent Bryozoa, on the other 

 hand, these buds might be expected to originate from the 

 ancestrula. A median primary bud is not indicated by any of 

 the sections. If it existed, it certainly arose from the ances- 

 trula. 



The size, shape, and position of the primary buds is beauti- 

 fully shown in figures- 38 and 39, and in the transverse sections. 

 These buds are long and tubular, and diverge but slightly from 

 the axis of the zoarium. There is no long vestibule as in 

 ephebastic zooecia, but the whole aspect of the buds is that of 

 a simple tubular zooecium, quite similar to that of the Cyclos- 

 tomata. There is also no indication of hemisepta or any other 

 structures within the zooecium. 



Secondary Buds. 



All buds of the second generation from the protoecium are 

 designated secondary buds. The series of sections (figs. 1-16) 

 seems to indicate that each of the primary buds produces a 

 lateral and a median bud. The lateral buds are very clearly 

 shown in such a position that they could have originated from 

 no other source than from the primary buds (see especially 

 figs. 5, 41, and 42). The median buds belong to the second 

 tier of zooecia. They are designated II n and 7/ 31 in figure 13. 

 The shape of the secondary buds is quite similar to that of the 

 primary ones (figs. 37, 45, 59, and 60). Figure 50 is a drawing 



different assumed orientation has convinced the writer that the zooecium in 

 question is a primary bud. To test this, four different bases in which the 

 protoecium and primary buds could be seen on the basal surface (in some 

 cases only after slight etching) were sectioned in the direction j — j, figure 

 48, which had been determined by previous inspection of the basal surface, 

 and marked by carefully drawing a fine line through the center of the pro- 

 toecium and as nearly as possible between the primary buds. Every one of 

 these sections has the appearance shown in figures 59, 60, and 45. It is 

 therefore unlikely that figures 19 and 20 (which were orientated at random) 

 represent the ancestrula. It is needless to state that only a very small 

 proportion of the many sections prepared in this study are figured. 



