THE AXIAL GRADIENTS IX HYDROZOA. 



to a new bud or branch before a hydranth develops at its tip 

 (see Child, '196, Fig. 10). These terminal regions of the cam- 

 panularian colony and of its branches are regions of relatively 

 rapid growth, each one representing temporarily a growing tip, 

 and reduce KMnO 4 rapidly and in large amount. In spite of the 

 .fact that it is covered with thin perisarc, the coenosarc at the 

 apical end of such a growing tip begins to stain earlier than any 

 other part of the colony except the tentacles and in some cases 

 the hypostome regions of hydranths. These growing tips and 

 the hydranth buds which develop at their apical ends always show 

 distinct basipetal gradients in rate of reduction, as indicated in 

 Figs. 3 and 4. In preparations cleared after reduction is com- 



4 



plete these parts in vigorous, rapidly growing colonies are usually 

 stained so deeply that they remain opaque even after clearing, 

 but these preparations show a much greater amount of reduction 

 in these terminal regions than in the stems. 



The Gradients in Stems. All parts of the stem are of course 

 enclosed in perisarc which increases in thickness basipetally. 

 Reduction of permanganate does occur to a slight extent in the 



