STRUCTUEE AND LIFE-HISTORY Of CRITHIDIA MELOPHAGIA. 197 



The Pre-flaa-ellate Stao-e. 



The early pre-flagellate stages of C. melophagia are 

 more or less oval or rounded bodies (PI. 12, figs. 1-6), varying 

 from 4*5 ju to 6 /x long, and from 1 ^ to 4"5/x broad. They 

 are most abundant in the fore-gut of young Melophagus, 

 but the pre- flagellate stage is passed through with great 

 rapidity and is easily missed. This probably accounts for the 

 very brief references to these small forms by Flu and Swingle. 



The protoplasm of the pre-flagellate forms is very finely 

 granular (Pi. 12, figs. 1-5). The nucleus is usually round 

 and not quite central in position (PI. 12, figs. 1, 9-12). The 

 bai'-like blepharoplast (kinetonucleus) is very deeply staining, 

 and lies eitiier below (PL 12, figs. 2, 10) or to one side of the 

 nucleus (PI. 12, figs. 1, 6). A chi'omatophile area with its 

 chromatin in a very diffuse condition is sometimes fairly 

 prominent, and from this a fine thread arises, which grows 

 outwards, forming the flagellum (Pi. 12, figs. 9, 10), and 

 appearing to draw out the end of the body with it (PI. 12, 

 figs. 11-13), while the periplast of the body forms the mem- 

 brane (PI. 12, figs. 14-20). The posterior end elongates at 

 t*he same time (figs. 16-18) and the flagellate form (PI. 12, 

 figs. 19, 20) is assumed. This. development is in accord with 

 that of C. gerridis and C. tabani, and I have watched these 

 processes in living specimens of both C. gerridis and C. 

 ni e 1 o p h a gi a . 



Division of pre-flagellate forms can occur before the develop- 

 ment of the flagella (PI. 12, figs. 8, 4). This will be described 

 in the section dealing with division. 



The Flagellate Stage. 



The mature flagellates vary very much in size, the variation 

 being due to division and growth. Very large forms (PI. 12, 

 figs. 44, 45) may be as much as 50 fi to 75 fi long, this measure- 

 ment including the flagellum,^ while short forms just flagel- 



^ It is almost impossible to differentiate between the limiting are as 

 of the body, the membrane and the free flagellum of C. melophagia, 

 as so much variation occurs in different specimens. 



