ifio] Robertson: Cyclostomatous Bryozoa. 23] 



zooecium; the third branch (6r. 3) on the ninth. If the ovieell 



is the seventh member (pi. 20, fig. 18), then the first branch 

 usually occurs on the third or fifth zocecium; the second branch 

 on the eighth, and the third branch on the eleventh zocecium., 

 although instances are found where the ovieell is the seventh 

 member, and the branching has taken place on the third, sixth 

 and ninth zocecia of the internode. The rule is, however, this: 

 the two upper branches, the second and third, keep a definite 

 relative distance above the ovieell; the second pairing with it 

 on the opposite side of the internode, and the third occurring 

 on the fourth zocecium above it, and hence on the same side of 

 the internode but on a zocecium adnate to the dorsal surface 

 of the ovieell. Further, the ooecial internode frequently curves 

 in such a way that the third branch begins immediately above 

 the median line of the ovieell, and the axis of the ovieell follows 

 the axis of the third branch rather than the axis of the internode 

 in which it belongs, while the remaining zooecia of this internode 

 continue in the original axis, and, carrying the zoarial tuft 

 upward, may send off a fourth branch considerably above the 

 ovieell. In their profuseness of branching these species show a 

 relation to C. ramosa Harmer, the ooecial internode of which may 

 give rise to six branches. 



In all the Crisias each zocecium in which a branch or inter- 

 node originates, consists of two parts separated by a flexible 

 articulation: a lower conical portion known as the basis rami 

 (pi. 18, fig. 2, ba. r.) adnate to the zooecium from which it orig- 

 inates, and an upper cylindrical portion which is more or less 

 free. These two parts are not independent but form integral 

 parts of the zocecium, the contained polypide when retracted 

 passing freely downward into the basis rami, and when expanded 

 passing as freely upward through the chitinous joint. The ooecium 

 (oe.), or ovieell and its contained embryos are clearly examples 

 of change of structure as adaptations to changed function. The 

 ovieell originates as does a zooecium, its place in the internode 

 being, as a rule, definite for a given species, and in correlation 

 with the zooecia of the internode. The tissue within the zocecium 

 is as clearly a modified polypide. This can be shown by an 

 investigation of the growing tips of branches where are found 



