PALMEN'S ORGAN ix HEPTAGEXIA AND ECDYURUS. 265 



mens seems quite untenable. Aside from the results of my 

 experimental work arises another question. Why should this 

 structure occur and persist in very small nymphs, and grow in 

 relative proportion during the comparatively long nymphal stage 

 of two, and in some cases three years, for the purpose of becoming 

 functional only after the nymph metamorphoses into its short- 

 lived adult stage, when all the other modifications which are of 

 a direct advantage to the adults develop during tin- comparath -ly 

 short time immediately preceding the- transformation:' 



The extent of the functions of this organ in the adults thus tar 

 remains unknown. Miall (1895) in >[>.. ikin- of the Kphenicrid.i' 

 gives the following quotation: "The n-cently eim-r^rd tl\ , " says 

 \><- Geer, "settles on trees, plant-, \\alls etc., lu-.ir the water 

 wliich harbored the larva. II- re it iiv- it-df by the hooks of 

 tin- feet, usually with the head downuanU. and rests until the 

 List or sub-imaginal moult is at hand." Mv o|,- ( r\ ation 

 tin- behavior of adult may-flies are to some extent in accord \\ith 

 i he. -i- of De Geer, however, no theory a> to tin- probable function 

 I the organ in the adults can be propounded, unless it can be 

 -upported by reliable results of experimental work. A I. 

 nuinber of nearly lull grown nymphs from \\hich the 1'aliiH n's 

 in had been removed are now in the aquaria \\ith tin- \i<-\\ of 

 making a study of their behavior, \\hen they emero- .1- adults in 

 comparison with that of the normal indi\ idual>. 



Among the twenty-three species in which 1'almen 1^77 noted 



t lie i ire-nice of this organ, there are se\ i al tin- -u immini; fi inns, 

 and at this time, it is difficult to say HIM \\hat |>art 1'alim-n's 

 m |>la\-s in those forms during their life history as \cr\- little 

 i> known of their natural habits. 



1 am greatly indebted to ProlV--or \\illiain S. Mar-hall for 

 su-v;-ting this problem, and also, lor his help and earnest interest 

 in the progress of the work. 



/< < M K.ICAL LABORATORY. 



UNIVERSITY OF \\'IM "\-i\. 



