380 KANSAS UNIVERSITY SCIENCE BULLETIN. 



longitudinal muscle; another in this same plane extends ven- 

 trally, supplying the legs; while another leads forward to join 

 the system again at the mesothoracic spiracle. 



At the mesothoracic spiracle we find a number of branches, 

 the direction of which may be best observed by referring to 

 the drawings. 



The mesothoracic spiracle lies well toward the front of the 

 thoracic box and might well be mistaken for prothoracic in 

 origin, but Taylor gives the following reason for considering 

 it mesothoracic : Immediately in front of the anterior thoracic 

 spiracle of the fly a well-marked apodeme or thickening of the 

 cuticle runs obliquely backward to the mid-ventral line, where 

 it unites with a similar thickening on the other side. The fore 

 leg of the fly is inserted on the body in front of this apodeme, 

 and muscles from the leg are attached to it. As the apodeme 

 approaches the mid-ventral line, it bears the ante-furca, which, 

 wherever it occurs, marks the junction of the pro and meso 

 thorax. The anterior spiracle of the thorax lies close behind 

 the apodeme which carries the antifurca, and is therefore 

 mesothoracic in position. 



Sexual Organs of the Female. The female Simulium, like 

 most other related forms, possesses two ovaries, which lie 

 on either side of the alimentary canal. (See Figs. 6 and 9.) 

 These may occupy only the caudal third of the abdomen in 

 case of the freshly emerged female, or take up all the available 

 space in the abdominal cavity, even crowding into the thorax 

 around the fore gut in case of females ready to oviposit. 



When the newly emerged female is examined, the ovary ap- 

 pears as a transparent pouch showing practically no differen- 

 tiation. But when this is removed and stained with borax 

 carmine the ova are deeply stained and are seen to lie in 

 regular order within the ovarian .sheath. As the ova mature 

 they lose their regularity of order and uniformity of shape, 

 so that by the time they mature they are but loosely joined 

 together and extremely irregular in outline. The latter is 

 brought about by their crowded condition in the body of the 

 insect. The eggs at maturity are relatively large, and when 

 we are able to count as many as 276 ova packed in the body 

 of a single female we do not wonder that they are so angular 

 in form. 



