1710 Journal of Applied Microscopy 



GENERAL PHYSIOLOGY. 



RAYMOND PEARL, University of Michigan. 



Books and Papers for Review should be Sent to Raymond Pearl, Zoological Laboratory, 

 University of Michigan, Ann Arbor, Mich. 



King, Helen Dean. Observations and Experi- This paper is a direct continuation of 



ments on Regeneration in Hydra viridis. previous work on regeneration in 



Arch. f. Entwickelungsmech. 13: n 15-178, tt 1 rr.i ^ xi 1 



jQQj " '^•^ Hydra. The present author endeavors 



to work out in detail important points 

 which have been left unsettled by other investigators. The experiments were 

 of two sorts ; (a) experiments on regeneration after simple injury, and (^) grafting 

 experiments, in which parts of two or more individuals were united. 



The technique of the operations is worthy of mention. In all the experi- 

 ments the common green hydra was used. All the experiments were made in a 

 shallow glass dish, bearing on the inside a thin coat of paraffin. The animals 

 were transferred to this dish and after they had become attached by the foot cuts 

 could be made in any desired direction with a sharp scalpel. " In all the graft- 

 ing experiments a fine glass thread was used to hold the parts of the graft 

 together, as bristles or hairs when delicate enough for this purpose are very flex- 

 ible and not readily pushed through the tissues without lacerating them. By 

 heating small glass tubing over the blowpipe flame it is easily drawn out into a 

 thread which can be made very fine and still firm enough to pass readily through 

 the tissues. The glass thread was always left attached to a piece of the larger 

 tubing which served as a handle in grafting, thus making the use of forceps 

 unnecessary. After the pieces of hydra had been brought together, the part of 

 the glass thread containing the graft was broken off from the handle and one 

 end stuck obliquely into the paraffin. The graft was therefore surrounded on 

 all sides by water, and, if the parts had been brought in close contact in the 

 beginning of the experiment, they so rarely separated that at least nine-tenths of 

 all the grafts were successful. In from one to two hours the components of the 

 graft were firmly united. The glass rod was then removed and the graft trans- 

 ferred into a small glass dish containing fresh spring water." In the dishes con- 

 taining the hydras green water plants were always kept and small Crustacea 

 (Daphnia, Cyclops, etc.) and Paramecia were given as food. 



Only a few of the more striking and important results of the experiments can 

 be summarized here, while for the numerous interesting details recourse must be 

 had to the original. Regarding the problem of the number of tentacles regen- 

 erated after injury the author concludes that both the size of the individual and 

 the size of the hypostome are important factors in determining the number of 

 tentacles in any given case. Double headed hydras were obtained by splitting 

 an individual longitudinally at the oral end. Such double headed individuals 

 always regenerated more tentacles than the original number. The two polyps 

 formed by longitudinal splitting always finally separate and each becomes a com- 



