236 



PSYCHE. 



[May 1895. 



On the other hand the retention of 

 sexual organs paired throughout, the 

 ducts remaining separate, with open, 

 paired outlets, shows that the May-flies 

 are, in this respect, more primitive 

 than any other winged insects. But as 

 regards the thorax and the wings, we 

 observe that in them a high degree of 

 modification has taken place. Thus 

 the two pairs of wings are very unlike 

 in size and shape, and this feature is 

 a secondary one. Hence the large 

 number of main longitudinal veins in 

 the wings of Ephemera is a case of 

 irrelative repetition of parts mostly 

 situated in the fan-like field, due to a 

 process of specialization, a process 

 which is manifested in quice another 

 way in the wings of the Dermaptera, 

 also a primitive type. Redtenbacher 

 regards the eleven longitudinal veins 

 (I-XI) of Ephemerids as the normal 

 number, and considers that the 

 Trichoptera, Lepidoptera, etc., have 

 lost certain of the veins by a 

 process of reduction. This view has 

 been adopted liy Comstock in his sug- 

 gestive paper, ■' Evolution and Tax- 

 onomy," but it seems to us to be 

 untenable, the anal field (" faltentheil " 

 of Spuler) not being of primary impor- 

 tance. On the other hand Redten- 

 bacher's use of Roman numerals for 

 the main veins, and of a combination 

 of Roman and Arabic numerals for 

 their branches, is very convenient. 



Spuler divides the wings of each pair 

 into an outspread portion {Spreiten- 

 tkeil), and a folded part (Falten- 

 theil). The veins of the former area 



he numbers in the same manner as 

 Redtenbacher, beginning on the costal 

 edge of the wing, while those of the 

 folded area (the submedian and internal 

 or first and second anal veins of other 

 authors) he does not name, but simply 

 numbers with Greek letters o P. He 

 considers that Hagen was right in 

 believing the Phryganidue, Tipulariae 

 and some Microlepidoptera to be forms 

 with a schematic, /. c, primitive vena- 

 tion (Stettin. Ent. Zeit., p. 316, 1S70). 



Spuler shares the opinion of Fritz 

 Miiller (Termitidae), Brauer and Red- 

 tenbacher (Libellulidae), and Haase 

 (Papilionidae), that the costa is only a 

 hypodermal structure, a thickening of 

 the edge, which does not have a 

 trachea as its origin (anlage), and 

 which therefore has nothing to do 

 with the veins. 



Spuler also shows that the venation 

 of the Orthoptera, especiallv their most 

 generalized form Blatta, is funda- 

 mentally nearly identical with that of 

 the Lepidoptera, veins I-V being 

 readily homologized with those of the 

 latter group ; so also with the most 

 generalized Hemiptera (Fulgora. Fig. 

 I). We mav also draw attention to 



the remarkable resemblance in the 

 venation of the generalized Psocid 

 genus Amphientomum, which at first 



