Printed in Great Britain The pattern of growth of Clytia johnstoni

1. A quantitative study of the growth of Clytia johnstoni is described. 2. The distance between hydranths is most commonly between 3 and 4 mm. The average internode lengths and their variability frequently differs not only between colonies but also between stolons of a single colony. The differences are therefore unlikely to be genetic ones. Occasionally much longer internodes occur (up to 8 mm). 3. Hydranths and their stalks differ widely in size but not in morphology. The differences can be caused by the amount of food given. 4. Very vigorous and very poorly growing colonies tend to have slightly longer internodes than the more common colonies of average vigour. 5. Most colonies produce both additional (secondary) hydranths and stolon branches. Hydranth branches grow spaced from existing hydranths; in normal colonies the spacing appears to originate from the hydranth away from the growing tip in an internode. In vigorous growth the hydranth towards the growing stolon tip is the place of reference. 6. Stolon branches occur mostly near to hydranths, either primary or secondary, more especially near to the hydranth farther from the growing tip of the main stolon