1915] Kofoid and Christiansen: On Giardia microti sp. iiov. 27 



rtagella. Connections with the free ventral flagella are not demon- 

 strable, but may be expected. The axostyle in G. microti is more 

 slender than in G. muris and is less expanded anteriorly. 



The parabasal bodies (par. b.) are two slender, tapering, curved, 

 deeply staining rods lying in the cytoplasm dorsal to the axostyle, in 

 the posterior half of the body. Their length is about 0.5 the trans- 

 diameter of the bod.y and the greatest diameter is 0.0.5-0.10 their 

 length. They usually lie parallel to one another and trend obliquely 

 posteriorly either to the right or left of the median plane. No 

 chromatic fibrils conecting these with the axostyle (blepharoplast?) 

 have as yet been detected in G. microti, though the presence of such 

 fibrils in G. muris is presumptive evidence that their detection may 

 be expected in G. microti also, in favorably located individuals. 



The peristome is a deeply chromatic strand in the rim of the 

 cytostome. It consists of two parts, an anterior arc (ant. perist.) 

 parallel to and often obscuring the intracytoplasmic part of the antero- 

 lateral flagellum, and a posterior part {post, perist.) pa.ssing in an 

 arc convex posteriorly from the lateral basal granule towards the 

 median plane to the region of the intracytoplasmic part of the postero- 

 lateral rtagellum. The peristome is subject to considerable variation 

 in volume and position and tends to disappear in stages of multiple 

 fission and encystment. 



Dimensions. — Length, excluding flagella. 10-16 /x; transdiameter 

 5-7 f/.; length of cysts 11-14 /j,. diameter 5-7 /x. 



Habitat. — Duodenum, ileum, colon, and rectum of Microtiis cali- 

 fornicus californicus (Peale) from Berkeley, California. 



Comparisons. — This species is nearest to Lamblia cunicidi Bensen 

 — the correct name of which is Giardia duodenalis (Davaine) — in 

 general proportions, but differs from it in the more tapering posterior 

 cone, shorter "tail," and in the more slender, more elongated para- 

 basals. It is also possible that the cytostome in G. microti more nearly 

 reaches the margin of the body than in G. duodenalis, though the 

 great mobility of this organ makes this character of less certainty than 

 the others above noted. 



It differs strikingly from the stout, rotund G. muris (Grassi) in 

 its more tapering, less convex posterior cone whose angle in G. microti 

 is 32°-55° and approaches 90° in G. muris. The paraba.sals in G. 

 muris are ellipsoidal bodies about half the length and twice the width 

 of those in G. microti. This difference alone is clearly diagno.stie. 



