68 Universihj of California Puhlications. [Entomology 



marginal vein. This condition is not common; it is best seen 

 in the front wing of the cockroach. 



Behind the primary vein all the veins except the marginal 

 lose their basal connections. The marginal vein is so delicate 

 at the extreme base that it is generally overlooked, and because 

 of its weakness it offered no obstacle to flexion, and so escaped 

 the fate of all posterior veins. Practically the whole difftculty 

 in homologizing veins arises from the difficulty in identifying 

 these posterior veins. How great these difficulties are, and 

 how completely we can follow these vagrant posterior veins, 

 will be shown as we discuss the different groups. 



This brings us to the consideration of a class of veins that 

 never has had basal connections. These we may denominate 

 i\\Q independent veins. The term "independent" has already 

 been used in Lepidoptera for these veins, and has never been 

 used in any other sense. The independents are most uni- 

 formly present in the area immediately behind the primary 

 vein, and have here been designated by Comstock and others 

 as the "media." Exactly similar veins may occur between 

 any two veins and develop in the same manner. These veins 

 may be designated by the vein immediately anterior to them. 



The independents arise from the margin of the icing, and 

 might possibly be considered as ingrowing branches of the 

 outer portion of the marginal vein; but, since this portion of 

 the marginal vein is commonly absent, while the independents 

 are almost always present, this conclusion may seem to be 

 unwarranted. In insects rich in independent veins, these are 

 produced wherever there is a sufficient space between two 

 veins, and they extend up the wing as far as the space remains 

 sufficiently wide. The order of their development in any 

 space (compare Fig, 23) is, first, the production of a vein 

 approximately half way between the two veins bounding the 

 area; secondly, one on either side of the first independent 

 vein, and then one in each of the four interspaces thus pro- 

 duced. This process might go on indefinitely, but generally 

 three or four ranks of veins are all that can be clearly recog- 

 nized, except in Ephemerida% where this system is most highly 

 developed. 



The relation of independent veins to branches is such that 

 it has given rise to confusion in the study of homology. In 

 the most typical condition the independent veins are strongest 



