34 BULLETIN 329, U. S. DEPARTMENT OP AGRICULTURE. 



28^ hours. One specimen which lived 23-| hours contained ovaries 

 with only a small number of eggs, about 25 in each ovary. One 

 adult which lived for 44 hours contained ovaries between the third 

 and fourth stages, and showed the transition from stage 3 to 

 stage 4 very clearly. Twelve adults contained ovaries filled with 

 fully developed eggs (stage 4, PI. I, fig. 4), ranging in num- 

 ber from 200 to 300. These adults .lived from 30 to 67^ hours. 

 Two adults contained ovaries with eggs of stage 4, but in small 

 numbers, about 50 in each ovary. They lived 48 ■ and 56 hours, 

 respectively, and possibly had developed the remainder of the eggs 

 left within the ovary after a previous oviposition. One adult con- 

 tained ovaries with eight fully developed eggs, and the remainder 

 of the ovary filled with eggs corresponding to stage 3. This adult 

 lived 34 hours and had presumably oviposited once, as is indicated 

 by the presence of the eight fully developed eggs, and then devel- 

 oped the remainder of the ovaries to stage 3. 



A comparative study of the ovaries of well-engorged (-| — | — \-) 

 specimens shows that no adult which died before reaching a period 

 of longevity of 30 hours after engorgement developed the eggs within 

 the ovaries to full degree. On the other hand, with one exception, 

 all adults which lived for 30 hours after engorgement developed the 

 eggs within the ovaries to the fullest extent. The fully developed 

 eggs within the ovaries were of the same shape as eggs freshly laid, 

 and only a fraction smaller. 



THE APPARENT EFFECT OF A BLOOD MEAL "UPON THE DEVELOPMENT OF THE OVARIES. 



In the studies which have been made of the ovaries of females of 

 Simulium venusturn under various conditions the following points 

 are worthy of emphasis: (a) In all adults taken while oviposit- 

 ing, apparently digested blood was found in the stomach, (b) No 

 eggs within the ovaries developed to the fullest degree without en- 

 gorgement and the requisite time in which to digest the blood meal. 



(c) The condition designated as stage 5 occurred both in adults 

 which had just oviposited and also in adults which were taken on 

 animals and killed at the time of capture. This condition (stage 5) 

 seems to furnish strong evidence that adults feed again after oviposit- 

 ing, as the majority of engorged adults showed the entire contents of 

 the ovaries developed. In addition the exact cause of the similar 

 condition found in adults which had just oviposited is known; 

 namely, that a few fully developed eggs were left in the ovaries after 

 oviposition and the remainder of the egg's were in a rudimentary" 

 condition apparently awaiting the necessary factors for development. 



(d) The males have reduced mouth parts and are not found engorg- 

 ing on blood, indicating the acquisition of this habit by the females 

 for a special purpose, as is the case with other blood-sucking Diptera. 



