LIGHT AS A FACTOR IN THE REGENERATION OF 



HYDROIDS 



SECOND STUDY 

 A. J. GOLDFARB 



Zoological Lahoralory, Columbia University, New York 



Three different kinds of hydroids are found abundantly in the 

 harbor of Woods Hole, Mass. Of these Tubularia (Parypha) 

 crocea reaches its most luxuriant growth about the end of June 

 and then declines in numbers and vitality toward the end of July 

 or the first part of August, at which time they disappear completely. 

 In the meantime Eudendrium ramosum begins to grow about the 

 first part of July, reaches its maximum growth about the end of 

 July and then gradually disappears. Pennaria tiarella comes 

 last, toward the end of July, and persists until the beginning of 

 September. All three kinds may be found on the same piles at 

 the same time. 



In a previous publication^ the curious effect of light upon the 

 regeneration of E. ramosum was described. From those studies 

 it was evident that the idea of the simple and direct effect described 

 by Loeb,- needed radical revision. In brief the facts for E. 

 ramosum are as follows. Under ordinary conditions, hydranths 

 are replaced in about 48 hours. As the hydranths live only a few 

 days, they are replaced again and again by new ones. If the 

 number produced on successive days be examined, it is found that 

 the largest numb^ are regenerated withm a few days after their 

 removal, and that the number steadily decreases on succeeding 



' Goldfarb, A. J. Experimental Study of Light as a Factor in the Regeneration of Hydroids. Journ. 

 Exp. Zool., vol. 3, 1905. 



- Loeb, J. The Influence of Light on the Development of Organs in Animals. Pfliiger's Archiv., Bd. 

 63, 1895. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 8, NO. 2. 



