3IO RESEARCH SEMINAR. 



ing expressed in the case under consideration by the abnormal 

 growth of the wing. The sections of these embryos show that 

 the parts of the brain posterior to the cerebral hemispheres on 

 the defective side were less developed than on the uninjured side, 

 owing to the absence of descending tracts from the cerebrum of 

 that side. This defect disappeared in the region of the medulla, 

 from which it may be concluded either that the tracts had de- 

 scended no farther, or that approximately half had decussated. 

 The trophic effect, if any, would be indirect, through the inter- 

 mediation of the motor neurons of the chord. Subject still under 

 investigation. 



A second series of experiments was made involving destruction 

 of the hind end of the embryo, showing, first, that there is no re- 

 generation, and second, that the uninjured embryonic parts de- 

 veloped precisely as they would have done in a normal embryo. 

 Thus, if but a single leg-somite remained, a rudiment of the leg 

 was formed in a developing embryo ; but if all the leg-somites 

 were destroyed no rudiment appeared. Absence of the allantois 

 was noted in such embryos. 



Other modifications of internal organs were described. 



22. Variation and Selection in Saturnid Lepidoptera. 

 By HENRY EDWARD CRAMPTON. 



An account was given of a study upon variation and. its rela- 

 tion to elimination in PJnlosaniia cyntkia, as well as of additional 

 studies which have been prosecuted during the past five years 

 upon the same, and other problems in the case of Cynthia and 

 othersaturnid moths. The first points determined were : (i) That 

 when normally formed pupae which died before metamorphosis, 

 were compared sex by sex with pupae which lived through the 

 metamorphosis, the two groups were markedly different in 

 several characters, as regards the typical condition as well as the 

 variability with reference to such typical condition. Thus pupal 

 elimination and variation were shown to be related. (2) A com- 

 parison of the pupne which metamorphosed perfectly with those 

 which formed more or less imperfect moths revealed a second 

 period of elimination which again proceeded hand in hand with 

 variation. Thus "secular" and "periodic" selection, so-called 



