1919] McCulloch: Life Cycle of Crithidia and Trypanosoma 155 



length, comparatively, of 32/z. At the other extreme, a short crithidia 

 of 7ju (pi. 2, fig. 12) is evidently mature, since it is undergoing a 

 process of multiple fission of the endogenous-budding type. Between 

 these extremes is a series of intergrading forms. The sizes and 

 shapes of a swarm of free crithidial flagellates from the life cycle 

 of anyone of these species of flagellates under discussion show great 

 diversity, and Crithidia euryophthalmi is not an exception, as indi- 

 cated in plates 2 and 4. The change in the appearance of the nucleus 

 as development proceeds is noticeable. The deeply staining mass of 

 chromatin (pi. 2, figs. 1, 2) becomes a nucleus containing a prominent 

 central karyosome and a chromatin-encrusted nuclear membrane (pi. 

 2, figs. 3-10). Between the karyosome and membrane is a clear area, 

 which destains very readily after iron-haematoxylin. 



MULTIPLE FISSION 



Endogenous budding. In looking over a large number of prepara- 

 tions of the digestive tract of Euryopkthalmus convivus, in the early 

 part of 1916, I chanced upon a splendid preparation of a "crop" 

 from a nymph which contained an exceedingly heavy infection of 

 crithidias of all shapes and sizes. The smear was well fixed and well 

 stained. 



Among other things the nuclear structure was studied in detail 

 to determine whether the nucleus of these crithidias divided by a 

 mitotic process or by a more primitive method of mitosis. This search 

 led to the discovery of a flagellate which apparently contained two 

 nuclei (pi. 2, fig. 12), in a linear arrangement with respect to the long 

 axis of the body. Shortly after another crithidia (pi. 2, fig. 13) was 

 found in the same preparation, containing apparently three similar 

 nuclei, which were arranged in a like linear series. In the latter 

 (pi. 2, fig. 13) careful focusing revealed the outline of a fourth 

 partially concealed beneath the most anterior nuclear structure. In 

 each of these flagellates (pi. 2, figs. 12, 13) no indications of any 

 ordinary process of binary fission were detected. The blepharoplast, 

 parabasal body, and the rhizoplasts in each were still intact in so far 

 as could be determined. The alternative hypothesis that these nucleus- 

 like structures, which are relatively small, are internal parasites of a 

 bacterial or protozoan nature naturally was given full consideration. 

 Drawings of these flagellates were made with the camera lucida and 

 the readings were taken for future reference. Owing to the abun- 



