1901.] NATURAL SCIENCES OF PHILADELPHIA. 127 



form of Calopteryx virgo, C. sj^leyidens, Pyrrhosoma minium, P. 

 ienellum, Agrion puella and pulchellum, Erythromma (najas), 

 Enallagma (cyathigennn), Ischnura (elegcms) and Platycnemis 

 pennipes, Lestes virens, Gomphus, jEschna, Anax, Corchdegaster 

 annulatus and hidentaius, Cordulia cenea, Diplax, Lihellula, 

 Orthetrum. 



The conclusions drawn by Dr. Ris from his investigations are as 

 follows : 



Larvce. — The original form of the gizzard shows a division into 

 sixteen longitudinal folds, eight broad and eight narrow, which 

 bear an armature of irregularly placed teeth. This type is found 

 in the Calopterygince. 



A higher development of the organ appears in the typical 

 group of the Agrionince ; the sixteen folds show a greater number 

 of teeth and a more complicated arrangement of these. 



The legion Lester shows a reduction of the sixteen folds to 

 eight, apparently through the loss of the smaller folds. These 

 eight folds are again divided into four broad and four narrower 

 folds. In i\\e Anisoptera {Gomphus and jE-ichna) there is reduc- 

 tion to four equal, similar folds. Finally, Corditlegaster and the 

 Libellulidce differentiate the folds into two pairs of teeth, so that 

 the original radial symmetry is changed to bilateral. 



Tmagos. — The series easily traced in the larval forms is some- 

 what confused in the images, owing to the reduction which inva- 

 riably occurs. The least reduction from larva to adult is found in 

 the Calopterygince; more is shown in the Agrionince, where is seen 

 the tendency to eliminate the smaller fold in certain individuals; 

 the strongest reduction occurs in Gomphus and jEschna; in 

 Cordulegaster and in the Libellulidce scarcely more than a hint of 

 the relation to the larva remains. 



This purely morphological development from the radial symme- 

 try of numerous elements of an organ to the bilateral symmetry of a 

 few elements runs parallel with the phylogenetic relationships of 

 the single groups. 



In a paper on the Odonata from Tepic, Mex.,* 1899, Dr. Cal- 

 vert gives notes on the gizzards of the forms studied by him. 

 Contrary to Dr. Ris and other previous writers, he finds the posi- 

 tion of the junction of fore- and mid-gut, and therefore of the 



^Proc. Gal. Acad, of Scieiices (Third Series, Vol. I, No. 12, 1899). 



