50 SOME MINUTE ANIMAL PARASITES 



like undulating membrane is produced at the elon- 

 gated anterior end, while that part of the thread 

 that forms the edge of the membrane continues as 

 the free flagellum. While extension is progressing 

 at the anterior end, the posterior end lengthens also, 

 and becomes somewhat club-shaped. The flagellate 

 stage is reached when the growth is complete. 

 Division may occur in the late pre-flagellate stage 

 (Fig. 9, E). 



The flagellate form of Crithidia pulicis (Fig. 10) is a 

 lengthened organism occurring chiefly in the mid-gut 

 of the host, where it moves with great rapidity. The 

 nucleus is oval, and the barlike blepharoplast is 

 near it. The root of the flagellum is near the 

 blepharoplast. C. pulicis, like other Crithidia, has 

 the nucleus in juxta- position to the blepharoplast, the 

 reverse being the case in trypanosomes, where the 

 nucleus is anterior to the blepharoplast. This is an 

 important difference between the two organisms. 

 The undulating membrane is very beautiful (Fig 10, C). 

 It is wide, and shows contractile threads in it. The 

 grace of the movements of the organism cannot but 

 be admired,' for the gentle ripples and easy turns 

 of the parasite display a remarkable balance and 

 rhythm. 



When the flagellate is full grown, it proceeds to 

 multiply by dividing into two lengthwise. As in 

 the trypanosome, division begins with that of the 

 blepharoplast, and following on that the flagellum 

 and membrane split. The nucleus becomes notched, 

 the two clefts deepen, the parts separate, and finally 

 the body substance becomes divided. The new forms 



