12 GUIDE TO CALIFORNIA INSECTS 



and remaining numerous in the older groups of insects but in the more 

 modern orders only a few of these are left, tho remaining a very important 

 element of the venation. 



Figure 6. Portion of the abdomen of an 

 ephemerid nvmph showing three tracheal 

 gills with wing-like gill covers and traces 

 of venation. 



Set. Ps^i 



Figure 7. Diagram showing possible 

 stages in the development of a venation. 

 A. primary vein. AM. anterior marginal. 

 PM. posterior marginal. lA. anterior. 1-4 

 P. posteriors. I. independents. B. branch. 



Figure 8. Diagram of thoracic structure. 

 Psc. prsescutum. So. scutum. Scl. scutel- 

 lum. Pscl postscutellum. Es. episternum. 

 Em. epimeron. St. sternum. 



Figure 5. (Opposite page.) Complex metamorpliosis, the development of Scu- 

 tellista cyanea, a parasite of the black scale. Beginning to the left above, the 

 figure shows egg, larva, pupa (back and side views), imago black scale overturned 

 showing four larvae, and two black scales showing exit holes made by the parasite. 



