36 



Drs. J. H. Ashworth and T. Kettie. 



[Sept. 28, 



as the lumen of the intestine is much too small to permit their passage 

 (fig. 10). When fully ripe, the cysts burst in the mid-gut, and their contained 

 spores are discharged with the faeces of the host. We have seen, in the mid- 

 gut of an adult flea, a ruptured, yellow cyst, from which some of the spores 

 (containing fully formed sporozoites) had escaped. The spores are dropped 

 by the host, and are ingested by the flea-larvae feeding among the debris in 

 the nest. We have several times found young trophozoites in the mid-gut of 

 larvae which had been hatched only two or three days. 



During the course of our experiments we procured a heavily infected series 

 of adult fleas, by rearing them in the laboratory, from larvae which we placed 

 in an old nest, in which a considerable number of infected fleas had been 

 kept and had died. Fourteen of these larvae were dissected, and all proved to 

 be infected; the rest were allowed to grow into adults, 11 of which were 

 dissected, and were all found to contain Gregarines. As six adult fleas from 

 the original nest in which the larvae were found, proved on dissection to be 

 uninfected, we think that we may reasonably attribute the occurrence of 

 Gregarines in every example of our laboratory-bred series to the fact that the 

 larvae had been reared in material which offered them a ready means of infection. 



Eipe spores, when placed in the fluid obtained by puncture from the mid- 

 gut of larval fleas, soon exhibit changes. The polar caps of each spore become 

 swollen and detached, leaving the rest of the spore like a barrel open at both 

 ends, from which the eight sporozoites escape. 



Each sporozoite is, when extended,* about 9"5 to 10*5 /x long, and 1*5 to 2 /* 

 in diameter at its widest part (figs. 12, 13). It has a slender, finger-shaped, 

 and mobile " rostrum," the organ by means of which fixation to the gastral 

 epithelium of the host is accomplished. The protoplasm of the sporozoite is 

 finely granular, and the nucleus is visible in the living condition. On fixing 

 and staining the sporozoites, the protoplasm was found to stain almost 

 homogeneously, except at the base of the " rostrum." where it was, in most 

 cases, coloured rather more deeply. The nucleus is large and vesicular. 

 Associated with its thick membrane are a few (four to six) small and deeply 

 stained chromatin masses. A karyosome is not present at this stage. 



We have not been able to observe the attachment of the sporozoite to the 

 epithelium of the larval gut, nor (as stated on p. 33) to determine whether 

 or not this is followed by an intracellular stage. There is evidence, however, 

 that the sporozoite, on fixation to the host, becomes more ovoid, that is, 

 shorter but broader, for, on the wall of the mid-gut of a young larva 

 (1"5 mm. long), we found a very young trophozoite, about 5 /j, long and 3 fi 

 broad. Whether this was attached to, or was within, an epithelial cell 

 * The body of the sporozoite can be bent into a curve or hook (fig. 12). 



