190 K. S. LASHLEY 



many generations in fresh water. The systematic hterature 

 and the studies of gonad production by Brauer, Downing Nuss- 

 baum, Weltner, and Koehtz, suggest the existence of monoecious 

 and dioecious varieties. The experiments of Tower show two 

 types of H. viridis differing in their reaction to the ultra-violet 

 rays (?) and in the time required for regeneration.^ Annandale 

 has described a variety of H. grisea from India which is char- 

 acterized by having a four-tentacled winter form producing 

 gonads. Whitney has been able to establish varieties of H. 

 viridis without green bodies. 



Summary 



To sum up the present section of the work : It has been found 

 that within a wild population of H. viridis there are hereditarily 

 diverse races which differ in their number of tentacles at sepa- 

 ration from the parent, in their size at a given age, and less cer- 

 tainly in other characters. The differences between such races 

 are permanent so long as the races are kept under the same 

 environment. The evidence favors the view that the differences 

 are truly genotypic (with the reservation that they are possibly 

 the result of differences in the age of the clones) . 



IV. INHERITANCE OF VARIATIONS WITHIN THE CLONE 



Inheritance of variations within the clone may be tested in 

 two ways; first, by an analysis of the resemblance between 

 parent and progeny by statistical methods; second, by a con- 

 tinued selection of variates, which should change the type of the 

 clone if the variations are inherited. As has been shown in the 

 discussion of Hanel's data, selection of variates within the clone 

 seems, on the average, to have no effect, yet there is usually a 

 positive correlation of parent and progeny with respect to the 

 selected character. Pearson has subjected Johannsen's data for 

 the selection experiment with beans to a similar analysis and 



" I have made many attempts to repeat Tower's experiments, using different 

 types of arcs, with and without interposed glass, but have never obtained the 

 sloughing of the ectoderm which he describes. 



