No. i.] STUDIES UP OX II YDROMEDUSAE. 49 



tacles, the body of the tentacle becoming the body of the 

 polyp, and in turn forming new tentacles. 



Nussbaum in 1887 and 1890 successfully everted specimens 

 and described the process by which the body layers righted 

 themselves. He secured no regeneration from detached ten- 

 tacles. 



Ischikawa in 1889 experimented upon eversion of Hydras 

 successfully and described the process by which the layers 

 readjusted themselves, differing in some respects from the 

 account of Nussbaum. 



In 1895 and 1898 Wetzel grafted specimens and secured 

 union between portions of same species ; but while bits of a 

 different polarity united, the distinctness of polarity was only 

 exceptionally modified. He secured only temporary unions of 

 portions of different species. 



Miss Peebles in 1897 undertook the determination of the 

 smallest portions of Hydra capable of regeneration. 



Rand in 1898 worked out interesting results on the "Regu- 

 lation " of regeneration in Hydra. 



Comparatively little has been done of an experimental nature 

 upon Hydroids. 



Loeb in 1891 carried on an extensive series of experiments 

 on regeneration and heteromorphosis among Hydroids, chiefly 

 of the genera Antennularia, Eudendrium, and Tubularia, with 

 the object of determining as far as possible the external con- 

 ditions and causes which affect life and growth. Light and 

 gravitation were shown to have a profound influence in deter- 

 mining many of the phenomena. 



In 1892 Miss Bickford conducted experiments on Tubularia 

 tcnclla, confirming in many points the work of Loeb. 



Davenport in 1894 conducted regenerative experiments upon 

 Obclia commisuralis, with a view to determining the distribu- 

 tion of generative or embryonic tissue in various regions of 

 the Hydroid. 



The contribution of the present writer to the general sub- 

 ject in 1897 has already been cited. 



Driesch in 1897 reviewed the work of Loeb and Bickford on 

 Tubularia. 



