ifl6| Kofoid-McVuUocli : Ti'ijixniosonia frinloinae 121 



These facts seem to indicate that in Triatoma the transformation 

 of the early crithidial phase into the haptomonad phase may take 

 place largely in the stomach, or at least that the transition forms 

 invade the stomach freely. 



5. The slender type. — Minchin and Thomson describe as necto- 

 monad forms certain slender, active, crithidial flagellates of the rectum 

 which i-eturn to the pylorus and there give rise to the terminal stumpy 

 trypanosome of the rectal type or remigrate to the rectum to carry 

 througli the same process. These are slender, active forms with ellip- 

 soidal, deeply and diffusely stained nuclei. We have not found indi- 

 viduals with this type of nucleus. If nectomonads occur in T. tria- 

 tomae. as we have figured it, they may be represented by the slender 

 type of our figure 22. 



IV. The Rectal Tryp.vnosome Phase 

 The cycle in the intestine of the invertebrate host terminates in 

 an infective form, a minute trypanosome which results from the 

 reverse transformation of the crithidial type back again to that of 

 the trypanosome. In Triatoma protracta these small trypaniform 

 flagellates have been found in great abundance in the rectum, where 

 they are in active locomotion. 



They are somewhat smaller than the merozoites of the stomach, 

 though attaining their size in some instances (cf. pi. 14, figs. 9-12, and 

 pi. 15, figs. 33-43). The transition from the crithidial phase to the 

 trypaniform is accomplished in the stumpy, rectal, crithidial forms 

 by the migration of the parabasal from its anterior position to one 

 posterior to the nueleiis (pi. 15, figs. 31-33), and the change in form 

 of the nucleus from a spheroidal to an ellipsoidal one. This process 

 continues with the gradual fading out and dissipation in a granular 

 chromidial cloud of the chromatic nuclear membrane and the central 

 karyosome (pi. 15. figs. 33-37), and the subsequent development of 

 the typical elongated, asymmetrical, granular nucleus shifted to one 

 side of the body (pi. 15, figs. 38, 39). The parabasal body in the 

 meantime decreases in size and migrates to the extreme posterior end 

 of the body (pi. 15, figs. 33^3). 



Minchin and Thomson (1915) include among the haptomonad 

 types of the rectal phase numerous small pyrif orm to spheroidal forms 

 in which there is no free flagellum but only a short intraeytoplasmic 

 shaft of that structure. We find also in the rectum of Triatoma 



