JOURNAL 



Jlf\a JBork ^Inj^omologiral HoriFig* 



\rol. VII. JUNE, 1899. No. 2. 



NOTE ON THE SECONDARY ABDOMINAL LEGS 

 IN THE MEGALOPYGIDiE. 



plate ii, figs. 1-3. 



By Harrison G. Dyar. 



I have contended that the additional pairs of abdominal legs present 

 in Megalopygidse on abdominal segments 2 and 7 are secondary struc- 

 tures, leading up to the form shown in the Eucleidae. Recently in 

 watching the progression of a larva of M. operciilaris on a smooth glass 

 surface, I observed that the parts of the feet bearing crotchets were not 

 used, but a small disk on the anterior side of each foot was applied to 

 the glass in the same way as the membranous feet of segments 2 and 7. 

 There is no disk on the last segment. Thus the Megalopygidse have 

 two distinct sets of abdominal feet, the normal ones, with crotchets, on 

 segments 3 to 6 and 10 and the secondary membranous ones, function- 

 ing more as sucking disks, on segments 2 to 7. The larvae are adapted 

 to walk both on rough surfaces with the r hooked feet, or on smooth 

 ones with the membanous disks. The structures which I mention have 

 been detected by Burmeister and accurately described. He says 

 that segments 2 and 7 have " un couss n rond aplati, qui res- 

 semble a la plante d'un pied ;" on segments 3 to 6 ** il y a un second 

 coussin plus grand, qui ressemble, a une veritable patte membraneuse 

 porvue d'une plante sineuse et d'une couronne de petits crochets cor- 

 nes;" on segments 10 a normal foot " completement conformee comme 

 les quatres moyennes des six anneaux anterieurs mais sans la petite 

 plante accessoire de celles-ci." I have italicized the important words. 

 Fig. I shows the ventral aspect of the membranous foot of M. opercii- 

 laris on abdominal segments 2 and 7 ; Fig. 2 the foot of segments 3 to 

 6 with the disk in front and the bent line of crotchets behind; Fig. 3 

 shows the normally formed foot of segment 10. I wish to emphasize 

 this interpretation of these peculiar abdominal feet, as I believe that it 

 shows very well the origin of the creeping disk of the Eucleidae. Me- 



