160 SIDNEY F. HARMBE. 



In A, B, and C of the above table the length of the internode 

 is measured from joint to joint, or from joint to apex of 

 branch if the internode is a terminal one. The " average 

 length" of the zocEcia is obtained by multiplying the length of 

 the internode by two, and dividing by the total number of 

 zooecia. It is obvious that this does not give the total length 

 of the zooecium, since the zooecia overlap one another; but an 

 approximation to the distance from mouth to mouth of the 

 zooecia is obtained. This gives a more accurate average than 

 any single measurement of this distance would give, since the 

 distance is variable in connection with the extent to which the 

 tubular apertures of the zooecia are developed, and with other 

 circumstances. For the purposes of this calculation an ovicell 

 is counted as an ordinary zooecium. If the length of the inter- 

 node of five zooecia shown in fig. 6 (C. eburnea) be compared 

 with that of a corresponding number of units, beginning at the 

 the base, of the ovicell-bearing internode in the same figure, it 

 will be seen that the presence of the ovicell does not affect the 

 result so much as would be expected at first sight, and the 

 error due to counting the ovicell as a zooecium is further 

 lessened by the fact that this structure is nearly always borne 

 on an internode which consists of many zooecia. 



In D the length is measured from any point of an aperture 

 to the corresponding point of the aperture of the next zooecium 

 on the same side of the internode, and in making this measure- 

 ment two zooecia whose tubular mouths were about equally 

 developed were always chosen. 



E gives the total length of zooecia with well-developed tubular 

 apertures from the point where their cavity disappears at their 

 proximal end to the furthest pointof their apertures, the measure- 

 ments being made from transparent (Canada balsam) speci- 

 mens. 



G is measured immediately above the aperture of a zooecium. 



H gives the length of the base with which a lateral branch 

 articulates. 



I. The length of the ovicell is estimated by drawing an 

 imaginary line joining the point where the zooecium next 



