200 



one and four, in the most central ones between three and nine. The number of 

 stem-internodes bears no particular relation to either the number of secondary 

 branches or to the number of zooecia in the latter. The number of stem-internodes 

 very rarely exceeds twelve, fifteen having been found only once in a very small 

 colony, the eight secondary branches of which had not yet any cylindrical inter- 

 nodes at the end. 



Growth. The youngest colonies I have seen consist only of a few stem-inter- 

 nodes, and that they have not been fragments is sufficiently evident from the 

 fact, that the apical internode had still but a very thin calcareous wall and ends 

 in a membrane. The examination of numerous young colonies in different stages 

 shows that such a colony is constantly increasing by direct growth, until the 

 separate zocecia-bearing secondary branches have attained to temporary comple- 

 tion by the formation of the apical cylindrical internodes ; however, in the differ- 

 ent colonies the secondary branches that have attained this temporary comple- 

 tion may contain rather a varying number of zooecia, and there may also be 

 found a rather great difference in the number of zooecia between the outer and 

 the inner secondary branches. In colonies with 13 — 15 secondary branches, the 

 number of zooecia of which varies between 2 and 9, this completion is probably 

 always attained, and often it may even be attained by colonies with 10 — 12 

 secondary branches, the number of zooecia of which is between 1 and 7. In all 

 younger colonies, however, a larger or smaller number of secondary branches is 

 found, which end in a funnel-shaped rudiment of a zocecium closed at the end 

 by a membrane, which is very rarely met with in secondary branches with more 

 than 5 zooecia. 



After the formation of the cylindrical terminal internodes a further increase 

 in the number of zooecia in the separate secondary branches may take place by 

 the transformation of these into zooecia, and this transformation may take place 

 in two different ways. In most cases a compressed, funnel-shaped body grows 

 from the basal part of the internode (figs. 6j, 6 m, 6 r) and surrounds the latter, 

 which increases in extent and gradually obtains a wider lumen. Time has not 

 permitted me to examine this development from stage to stage; but the various 

 stages I have seen leave no doubt of the fact, that this funnel-shaped rudiment 

 is the beginning of a zooecium, as, apart from the cylinder arising from its centre, 

 it quite agrees with the zooecial rudiments which arise by direct growth. In the 

 other, less frequent case the transformation takes place by a gradual swelling of 

 such an internode (figs. 6 n— 6 q), which is by and by furnished with an oval 

 depression, presumably corresponding with the cryptocyst depression of the zooe- 

 cium, and further forward with a distal wall. Both these forms may be found 



