A PARASITE OF THE HUMAN FLEA 49 



frail-looking, oval organism (Fig. 9, A t B), becoming 

 more elongated as it ages. It has a large, distinct 

 nucleus and a barlike blepharoplast. The pre- 

 flagellate often shows a special area which will 

 stain intensely, and so may be termed the chroma- 

 tophile area. The contents of this area at first are 

 finely granular, but little by little the granules 

 collect and form a thread which at first is tightly 



FIG. 9 CRITHIDIA PULICIS: STAGES LEADING TO THE 

 FLAGELLATE FORM 



A , 5, Typical oval pre-flagellates ; C, rosette of elongating pre- 

 flagellates ; D, single form separated from rosette ; E, dividing 

 form 



coiled up, but which gradually loosens its coils and 

 reaches the surface of the body. Simultaneously the 

 body of the pre-flagellate commences to grow, and as 

 it elongates, the thread uncoils and presses outwards 

 (Fig. 9, C, D). The limiting layer of the body, 

 moreover, is elastic, and, under the pressure of the 

 firm thread, moves with it, and gradually the fin- 

 4 



