360 E. R. CTIMINGS POSITION OF THE ^^O^TI(•rLT^OROTDS 



teriorly, whereas the otlier tliree are direeted anteriorly — that is, in the 

 direction of the aiieestrula. In some of the sections another bud is seen 

 between e and f, and probably originated from one of them. In the ver- 

 tical sections (figures 20-24, 33, and 35) the fact is revealed that these 

 two buds {e and /) arise at a level somewhat above the substratum, and 

 serial sections show that they lap well past the ancestrula and arise to 

 one side of it. As they attain the vertical ascending position, they swing 

 in toward each other and ride over the superior surface of the protoecium 

 (figures 3-6). 



All of these buds give rise, as in the case of the ancestrula, to vertical 

 successions of superimposed zooecia — the zooecial tubes of the colony. 

 The upward extension of bud e (or /) is beautifully shown in figure 21 

 (also figure 35). Diaphragms and cystiphragms begin very near the 

 point of origin of the tube. The wall structure of e and / is different 

 from that of the ancestrula and like that of all later zooecia. The wall 

 structure of the posterior portions of the lateral primary buds (2 and 3) 

 is similar to that of the ancestrula and protoecium. In fact these buds 

 and the protoecium are very sharply set off by this characteristic thick- 

 ened wall from all of the buds posterior to them (cf. figures 14-16). I 

 believe that the only interpretation of this feature is that this portion of 

 the young colony was exposed while the lateral buds of the second and 

 third generations were developing and before any of them came into 

 contact with it. During this interval the exposed wall became more or 

 less thickened and covered with foreign particles. This last fact is dis- 

 closed by the presence frequently in the sections of minnte opaque parti- 

 cles lying in this region of the infantile zoarium (nepiasty), such as are 

 commonly seen in sections through the surface portion of Trepostomata. 

 The thickened posterior wall of the nepiasty is a very constant and emi- 

 nently characteristic feature in sections of all the genera in which the 

 initial region has been studied. Where the lateral buds of later genera- 

 tions envelop the nepiasty loosely, as shown in figure 17 {Callopora ?), 

 this whole regioii is filled with foreign material. 



THE SECONDARY BUDS 



The exact origin of the two buds e and / can not be ascertained. From 

 the analogy of recent Bryozoa they might come from either buds 2 and 3 

 or from the buds lying to the right and left of them {z-z\ figures 25-27). 

 These two possibilities are shown diagrammatically in figures 26 and 27, 

 where the solid arrows show the most probable arrangement and the 

 broken arrows the alternative interpretation. The direction and charac- 



