178 University of California Publications in Zoology [Vol. 19 



tion of the parasites into the final spore forms and the ordinary 

 propagative forms takes place apparently in the stomach phase in 

 the "crop." The majority, in fact, nearly all of the parasites become 

 ordinary propagative forms which develop and increase their num- 

 bers in the digestive tract of the lupine bug. After passing through 

 the various processes of the life cycle they degenerate in the late 

 rectal phase in the pyloric expansion. The permanent rectal phase 

 persists through the life of the lupine bug after the first infection ; 

 the degenerative series is soon formed, and likewise persists throughout 

 the life of the host. 



The individuals of the degenerative series are distinguished among 

 the mass of living crithidias by a sticky periplast, to which bacteria 

 frequently adhere by virtue of the tendency of crithidias to adhere to 

 each other, by slow sluggish movements, and by odd sizes and shapes. 

 The degenerating forms are detected in stained preparations by nuclei 

 with diffused chromatin or by a vesicular nucleus breaking up into a 

 number of chromatin granules, and by the vacuolated cytoplasm. The 

 size, shape, and location of the crithidias also assists in distinguishing 

 between the developmental and degenerative crithidias. 



CONCLUSIONS 



1. The crithidial flagellates of the life cycle of Trypanosoma are 

 structurally like the crithidial flagellates of the life cycle of Crithidia. 

 The extranuclear organelles, the blepharoplast, parabasal body, para- 

 basal rhizoplast, nuclear rhizoplast, and the flagellum are all common 

 to the crithidial flagellates of both Trypanosoma and Crithidia. 



2. From the viewpoint of comparative morphology the differences 

 existing between the crithidial forms of C. curyophthalmi and the 

 crithidial forms of T. lewisi are less marked than are the differences 

 between similar stages of T. lewisi and Schizotrypanum cruzi. 



3. Using the life cycle of T. lewisi as a standard for comparison of 

 the life cycle of a haemoflagellate or a trypanosome and the life cycle 

 of C. euryophtlialmi as the standard of the life cycle of a more primi- 

 tive crithidial flagellate, there are more parallel stages and phases in 

 these two life cycles than exist between the life cycle of any trypano- 

 some and the life cycle of any herpetomonad or of any leptomonad now 

 known. Furthermore the close correlation between these two life 

 cycles of T. lewisi and of C. euryophthalmi affords new evidence that 



