44 THOMAS L. BANCROFT. 



grown to a remarkable size and can be easily seen in the malpighian 

 tubes and are capable of slight movements. In eighteen to twenty 

 days they have arrived at maturity as far as their life in the 

 mosquito is concerned; they have left the malpighian tubes and 

 lie in the alimentary canal about the head also in the labium; they 

 are 2V inch in length by T %o inch in breadth. 



If the proboscis of a filariated mosquito be cut off and mounted 

 on a glass slide in water with cover-glass, and examined under the 

 microscope, a slight pressure on the cover-glass being applied to 

 cause the stylets to leave the labium, the young filarial may be 

 seen swimming up and down the apparent canal in the labium 

 [what Grassi designates "the prolongation of the general cavity 

 of the body within the labium]; a little further pressure on the 

 cover-glass causes the worms to escape at the extreme end of the 

 labium. Whether there be a natural opening at the labellar end 

 of the labium seems doubtful, but in every instance in which the 

 experiment was made the young filarial escaped at this point, and 

 at no other. 



In several works on entomology, giving descriptions of the 

 mouth organs of dipterous insects, [that are in my possession] there 

 is no mention of a canal in the labium or of any opening at the 

 tip. It seems to me that should no natural opening exist at the 

 spot indicated, the young filaria would have very little difficulty 

 in making one, and I believe that they naturally do leave their 

 intermediary hosts at this point; here they could wriggle into the 

 wound made by the mosquito and would avoid any risk of being 

 sucked up with the blood. 



The young filarial placed in water wriggle about but are quite 

 unable to leave the spot where they happen to lie; it is not 

 unreasonable to conclude that, as they are so helpless in water, 

 they could scarcely swim against the blood stream entering the 

 mosquito. There is still another objection to Grassi's idea of a 

 rupture; this occurs when the labium is "stuffed with nlarise," but 

 it would not be likely to happen when the labium contains a single 

 worm as is frequently the case. 



