Light in the Regeneration of Hydroids 135 



manner just described, and kept in a dark chamber. The manipu- 

 lation, change of water and counting of hydranths of the latter 

 stalks were all done in the dark room, into which the only light 

 was that which came through a double thickness of ruby glass. 

 The temperature of the controls varied slightly from the others, 

 the difference never exceeding 2 to 2|° C. As each new hydranth 

 was fully developed it was removed. Thus the figures in the 

 tables represent the actual number of regenerated hydranths. 



TUBULARIA (pARYPHA) CROCEA 



This is a colonial hydroid usually made up of unbranched 

 stalks, though not infrequently small branches are developed. 

 Stalks were cut off quite close to their bases, their hydranths were 

 then removed at approximately the same level for all the stalks 

 of a series, i. e., either at the base of the hydranth or the middle of 

 the stalk, etc. The results obtained among the controls and 

 among those maintained in the dark chamber are given in the 

 accompanying table. 



In Experiment i, the hydranths were removed about five- 

 eighths inch from the apical ends. No branching stalks were 

 used. The 24 controls were prepared in the light, 40 others were 

 prepared and kept in the dark. In Experiment 2, there were 20 

 controls, and 42 in the dark. In Experiments 3 and 4, all hydranths 

 were removed in the light. In Experiment 3, there were 20 con- 

 trols, 60 in the dark. In Experiment 4, the hydranths only were 

 removed, leaving one part of a colony of about 50 stalks, con- 

 nected at their bases, to serve as a control, and another part of 

 the colony was placed in the dark. In all there were 114 controls 

 and 192 in the dark. 



As in E. ramosum, the hydranths are regenerated ordinarily 

 within two days after their removal. In the dark, their first 

 appearance was somewhat delayed, though all subsequent regen- 

 eration took place at the normal rate. This initial retardation 

 is seen in Experiment i, where 24 controls regenerated 21 hy- 

 dranths on the second day and i on the third day. The 40 kept 

 in the dark regenerated 5 on the second day, while 23 appeared on 



