1910.] MORPHOLOGY OF EIMERIA AVIUM. 675 



the intestinal epithelium^especially of the duodenum— and so 

 begin a new infection. Thougli the oocysts and spores are the 

 most obvious external manifestation of coccidiosis, it is usual 

 and certainly more convenient to begin the life-cycle of the 

 Coccidium with the minute sporozoite (PL LY. fig. 2), the agent 

 whereby primary infection is bi'ought about. 



(a) The young, growing Parasite. 



The sporozoites are minute, fa.lcifoi'm or vermicular bodies 

 (PI. LV. fig. 2) capable of fairly rapid movement and possessing 

 great penetrative powers. They measure from 7 yu to 10 /^ in 

 length. The ends of the sporozoite are rather pointed, the 

 extremity that moves foremost being slightly more acuminate 

 than the posterior end. The general body cytoplasm is more or 

 less homogeneous, exhibiting but very fine granulations. The 

 nucleus has a definite rounded or oval contour. The chromatin is 

 evenly distributed throughout the nucleus. 



When the sporozoites are liberated from the investing sporocyst 

 (PI. LVIII. figs. 74-76), by the action of the pancreatic juice of the 

 grouse, they are capable of active movement. The usual method 

 of progression resembles that of the sporozoite or motile tropho- 

 zoite of a Gregarine. The organism moves forwards with a slow 

 gliding movement, the forward progression being facilitated ])y 

 the secretion of a viscid proteid substance that I'apidly hardens. 

 On the smooth surface thus provided the coccidian sporozoite 

 glides forward. The ti'ack of the spoi-ozoite, as shown by its trail, 

 can be stained, and the organism then shows the ge]a,tinous or 

 proteid material issuing from near the posterior region of its 

 body (PI. LY. fig. 2). During the gliding movement waves 

 travel down the body of the spoi'ozoite, recalling what is seen on 

 a larger scale in the billowy undulations of the foot of a snail. 

 On other occasions a more rapid movement of the sporozoite 

 occurs. The two ends of the organism become approximated and 

 then rapidly straightened, the eflect being to propel the oi-ganism 

 forwards much more quickly than when the gliding movement 

 alone is used. 



The sporozoite thus makes its way to an epithelial cell of the 

 duodenum and proceeds to peneti'ate the cell. As it forces its 

 way inwards (PI. LY. figs. 3, 4), so the spoi'ozoite curves on itself 

 (fig. 7) and becomes round and immobile (figs. 5, 6, 8). The 

 young, rounded parasite (figs. 8-10) is now in the trophic phase 

 of existence and continues to grow for some time, feeding passively 

 on the food-materials of the host-cell. During this period the 

 parasite is called a ti^ophozoite (figs. 8-12 «). 



The nucleus of the trophozoite is approximately central in 

 position, or sometimes to one side, and at first contains scattered 

 granules of chromatin. It then becomes somewhat vesicular 

 (figs. 8-11), and gradually the chromatin collects into a central 

 karyosome. lying within the nuclear sap (fig. Via). The position 



