HOST-PARASITE SPECIFiaTY IN THE GENUS GIARDIA 147 



a method for the cultivation of members of this genus be worked 

 out inasmuch as past experience has shown that the abiHty to 

 cultivate an organism aids tremendously in the growth of our 

 knowledge of that organism. 



PROBLEMS FOR STUDY 



a. Morphology of the trophozoite. Inasmuch as our conclusions 

 with respect to host-parasite specificity in this genus depend upon 

 our ability to recognize different species and since the recogni- 

 tion of species requires a detailed knowledge of morphology it is 

 important for us to be famihar with the structure of both the 

 trophozoite and the cyst. As indicated in Fig. 14, the trophozoite 

 possesses a large ventrally located sucking disc. There are two 

 nuclei present. These are attached by rhizoplasts to blepharoplasts 

 at the anterior ends of the two axostyles. The writer believes that 

 there are two thread-like axostyles, as indicated in the illustration, 

 with a single blepharoplast at the anterior end of each. Certain 

 investigators (Kofoid and Swezy, 1922) believe that there is a 

 single axostyle and others (Wenyon, 1926) believe that there are 

 two blepharoplasts at the anterior end of each axostyle. Further 

 study is necessary before one or the other of these views is estab- 

 lished. Between the blepharoplasts at the anterior end of the axo- 

 styles is an interblepharoplastic rhizoplast in the center of which is 

 an interblepharoplastic granule. The four pairs of flagella are 

 located as indicated in Fig. 14. The antero-lateral flagella extend 

 forward from the blepharoplast and appear to cross near the an- 

 terior end. Kofoid (1922) suggests that a chiasma does not really 

 exist at this point but that the two flagella simply come into con- 

 tact without crossing. The shield-shaped areas on either side of 

 the body are known as lateral shields. The region extending from 

 the point where the posterior lateral flagella emerge from the body 

 to the posterior end is often referred to as the tail. Near the center 

 of the body are one or two deeply staining structures known as 

 parabasal bodies. 



h. Morphology of the cyst. Cysts of Giardin that are properly 

 stained reveal two, four, eight or more nuclei which are distributed 

 with two near the anterior end or two near either end or four near 

 the anterior end or four near either end. Multinucleate cysts of both 

 trophozoites and cysts of Giardm muris and Giardia microti have 

 been described by Kofoid and Christiansen (1915). Within the cyst 



