THE CANADIAN ENTOMOLOGIST. 407 



histoblasts so accelerated that the pupal, or in some cases adult, 

 organs appeared as external structures in the as yet immature 

 larvae. Such cases have been recorded by Heymons ('Oo) in Tene- 

 brio molitor, Hagen ('r2) in Bombyx mori, and others in various 

 Coleopterous larvae. A study of the cases of prothetely now on 

 record shows that they were all produced under artificial conditions. 

 This would suggest that it is due to some pathological disturbance, 

 which has caused an excessive stimulation of the enzymes, whose 

 action brings about the multiplication of adult tissue forming cells, 

 without appreciably affecting those of the larval tissues. It then 

 follows that there are two sets of enzymes concerned in the matura- 

 tion of holometabolic insects, one of which may be termed the 

 "larval enzymes" and the other the "adult enzymes." The sup- 

 pressed growth of the histoblasts in parasitised Simulidse would 

 then be due to the worm decreasing the stimulating action of the 

 adult enzymes by impoverishing them either in quality or 

 quantit}-. This subject is discussed more fully in an earlier paper 

 by the writer ('11), where this pathological condition is termed 

 Methetely, in contradistinction to Kolbe's Prothetely. 



The parasitised Simuliid larvae are unable to pupate and are 

 finally killed by the worm, which bores its way out through the 

 "skin" and thus escapes into the water. Here it probably leads a 

 free sexual life, as do the related nemathelminths found in grass- 

 hoppers of which it is only the larvae that are parasitic. It is sur- 

 mised that the larval worm passes into the body cavity of its host 

 from the alimentary tract, into which it would be readily taken 

 with the food. This worm was found during the spring in varying 

 abundance in most of the streams examined. The largest percen- 

 tage of infection was 25, equally distributed between the two 

 species of Simulium present in that stream. It was never found 

 in the fall, and has probably one generation only per annum. 



During the spring there was a very high percentage of para- 

 sitism by various Myxosporidia S. L. (Sporozoa). When these 

 were discovered, they had all sporulated, and were therefore at too 

 late a stage in development for their taxonomic position, or life 

 history, to be ascertained, but they were evidently related to the 

 organisms causing the Pebrine disease of silkworms. The body of 

 tiie parasitised larva becomes enormously distorted and swollen, 



