144 University of California Publications in Zoology [VOL. 19 



THE COMPARATIVE MORPHOLOGY OP CRITHIDIA AND 

 THE CRITHIDIAL STAGES OF TRYPANOSOMA 



The morphology of Crithidia and Trypanosoma has been the sub- 

 ject of careful investigation for a number of years, and our concep- 

 tion of the structure of these simple organisms has been modified from 

 time to time by additional discoveries. This is especially true of 

 the extranuclear organelles of these flagellates, owing to the recent 

 investigations carried on in the Zoological Laboratory of the Uni- 

 versity of California by Dr. C. A. Kofoid (1916) and Dr. Olive 

 Swezy (1916), the latter studying particularly the binuclear theory 

 of Hartmann (1911). The work of these investigators has centered 

 attention upon the extranuclear organelles of these flagellates, con- 

 sisting of the blepharoplast (fig. A, U.) at the base of the flagellum, 

 the parabasal body (pb.), or kinetonucleus, the rhizoplast (r/.), the 

 parabasal rhizoplast (pb. rh.), the flagellum (fl.), and the undulating 

 membrane (und. m.). They have homologized the kinetonucleus of 

 the Protomonadina (Herpetomonas, Crithidia, and Trypanosoma} 

 with the parabasal body of the Polymastigina and the Hypermasti- 

 gina. Bearing this in mind, it at once becomes clear that this extra- 

 nuclear complex of organelles is the neuromotor apparatus of Crith- 

 idia and Trypanosoma (Kofoid, 1916). In a previous paper (Kofoid 

 and McCulloch, 1916) the term parabasal body was used in place of 

 kinetonucleus throughout and I shall employ this nomenclature in 

 the present paper. 



The position of this extranuclear complex of organelles determines 

 largely whether the flagellate is a trypanosome or a crithidia. The 

 trypanosome is characterized by the presence of the parabasal body 

 and the blepharoplast posterior to the nucleus, and by a well developed, 

 undulating membrane which passes forward laterally along the edge 

 of the ribbon-like body. These characteristics are common to the 

 flagellates found in the blood, and modifications of this structure take 

 place as soon as the medium is changed, as in the transfer to the 

 stomach of the flea. The transition stages between a trypanosome and 

 a crithidia have been designated as crithidiomorphic trypanosomes by 

 Minchin and Thomson, as previously noted. In the transition forms 

 the parabasal body and the blepharoplast are still posterior to the 

 nucleus at a greater or less distance, but the movement and shape of 

 the body of the flagellate are distinctly like those of a crithidia. In 



