REMARKS ON THE STRUCTURE OF GREGARINyE. 349 



number of cleavage products ; but I have only once in the 

 examination of many hundreds of specimens of Tubifex found 

 cysts containing fully-formed pseudo-naviculro. 



In this case there Avere some dozen or more cysts, most of 

 Avhich were crowded Avith pseudo-uaviculee. These were so 

 numerous that, when the cysts were burst by pressure, the 

 whole of the area covered by the thin glass square, the side 

 of which measm-ed half an inch, was peopled with them. 

 These pseudo-naviculse had the form seen in fig. 19, namely, 

 an oblong head Avith a stiff, sharp curved process of three or 

 four times its length projecting from one end of it. I was 

 unable to ascertain the further development of these bodies, 

 but found that they possessed a marked tendency to adhere 

 to foreign bodies which were sufficiently soft to admit of 

 penetration by the stiff motionless filament. In this way 

 several penetrated an uninfected Tubifex, which I placed in 

 a small cup of water, together Avitli a quantity taken from 

 the specimen above mentioned. 



I was not able to folloAV directly the development of the 

 contained protoplasmic mass of the pseudonaviculte of 

 Monocystis slpunculi. I, hoAvever, found certain organisms 

 on several occasions in partially broken-doAvn cysts, and in 

 the curious little diverticulum of the alimentary canal near 

 its rectal portion — a site Avhicli is not unfrequently affected 

 by encysted Gregarina3 — which I take to be the pseudo- 

 filarial stage of the M. sijnmculi. I have the less hesitation 

 in considering them to be of this nature, because I frequently 

 obtained them in great numbers from this diverticulum 

 associated Avith numerous, A'ery small, but perfectly indis- 

 putable Gregarinre, such as is the one draAvn in fig. 18. 

 The organisms in question Avhich ofteu Avere exceedingly 

 abundant in particular masses of tissue appearing to be old 

 cysts, or in the before-mentioned intestinal diA'erticulum, 

 measured from the -^-^'^y-^th of an inch upwards in size, 

 aA'eraging the --^^-^th. They Avere minute, oblong flakes of 

 protoplasm, devoid of all nucleus or other structural differen- 

 tiation, broad and rounded at one extremity, tapering and 

 draA^'n out almost to a thread at the other (fig. 7). Their 

 movements Avere incessant, consisting in the oscillation from 

 side to side of the tapering extremity. The vibrations of 

 this portion Avere so rapid that I at first thought that a fringe 

 of long cilia existed on the sides of the posterior elongation 

 of the little organism. I afterAvards satisfied myself that 

 they have the form seen in fig. 7. Whether an amoeboid 

 condition precedes this I am unable to say ; but I look upon 

 these active, Avriggling cytods (for they are not yet cells) as 



