140 PROCEEDINGS OF THE ACADEMY OF [JaU. , 



A marked exception to thi;; was found in the genus Heteragrion. 

 Of four species of this genus, three had sixteen folds, varying 

 in size, tlie largest folds bearing numerous teeth (above forty;, 

 the smaller ones bearing from five to thirty, while the fourth 

 species had but eight folds, each fold bearing numerous teeth. 



Again, of four species of Argia, three are similar, bearing 

 eight " F" folds and eight " f " folds, the teeth on all folds 

 being of equal size. But in the fourth species, A. agrloides, there 

 are four " F" folds, eight " f " folds, and four "f" folds; on 

 the two lalt.er the teeth are equal in size, but on the four " F " 

 folds they are arranged in two groups, those of the anterior group 

 being similar to the teeth on the other folds, those of the posterior 

 being much smaller and recurved. 



Data for Phylogexy. 



When the studies whose results are contained in the present 

 paper were begun, it was hoped that they would yield data of 

 value in determining the pbylogeny of the insects investigated. 

 The data are now at hand, but the desired interpretation is yet to 

 be made. One may spin several difierent theories on the lines of 

 descent of these Odonata if regard be had merely to the armature 

 of the gizzard. Bui since these theories would rest on precisely 

 the same evidence in each case, it is wise to refrain from such 

 theorizing until these results can be correlated with others drawn 

 from embryological and comparative anatomical data. 



It is worth pointiug out, however, as one present gain to our 

 knowledge which will bear on the question of phylogenies, that the 

 occurrence of numerous minute teeth only is a phenomenon of 

 frequent repetitiou, since it is met with in the genus Hetcerina of 

 the legion Caloptenjx, and in all species of the legions Evphoea 

 and Thore of the Calopterygince, while in the Agrionince it is ob- 

 served in Jlecistogader and Pseudostigma (legion Pseudostigma) , 

 Philogenia (legion Podagrion), some Disparoneura and Caconeura 

 (legion Proloncura) and all of the legion Lestes. 



The problem which this phenomenon suggests is to determine 

 whether it represents a more primitive condition, originally common 

 to all groups to which the genera named belong, or whether it 

 represents independent, parallel and similar modifications in each 

 group from some other and different form of gizzard-armature. 



