3l8 A.J. Goldfarb 



the kind of regeneration in other hydroids. In the following study 

 of Eudendrium ramosum, I have attempted to examine nearly all 

 the known factors, external and internal, that enter into the life 

 of this hydroid, especially those that take part during growth and 

 regeneration. 



Eudendrium ramosum consists of one or more main stems, bear- 

 ing pinnately arranged lateral branches which, in turn, branch again 

 and again, finally ending in pedicels each bearing a polyp. When 

 kept in an aquarium the polyps disappear and regenerate period- 

 ically. A few preliminary experiments made it clear that the 

 method,- previously used, of adding the number of hydranths 

 regenerated on a stem, each successive day after amputation ot 

 the polyps, did not give an accurate idea of the actual number of 

 different hydranths regenerated in a given time. If, for example, 

 one or more hydranths should regenerate on a branch at about 

 the same time that an equal number of other hydranths degener- 

 ated, the records would not show the formation of new polyps. 

 In the following experiments the exact number of different 

 hydranths produced each day was recorded by the aid of daily 

 diagrams of each stem and branch showing the presence or 

 absence of polyps, buds and stolons. 



Hydranths appear within two or three days after amputation. 

 Later some or all of the regenerated hydranths may disappear to be 

 replaced in part or in whole by new hydranths; or other cut ends, 

 devoid of hydranths, may regenerate them now for the first time. 

 In order to condense into the smallest space the data essential 

 to an understanding of the phenomena, the number of hydranths 

 that appear within three and six days respectively, after the removal 

 of polyps, are quoted in the following tables, unless specifically 

 mentioned to the contrary. When fractions are used the numer- 

 ator represents the number of new hydranths formed in the time 

 stated; the denominator indicates the number of lateral branches 

 or pedicels removed. For convenience these fractions are usually 

 reduced to per cent. 



It is nearly impossible to obtain stems absolutely alike in all 



•'Light as a Factor in the Regeneration of Hydroids: Goldfarb, Journ. Exp.ZooL, 1906. 



