1878.] the Life-History of a Minute Septic Organism. 337 



nules is formed, at first faintly, and afterwards very distinctly, which 

 is shown at a, fig. 11. In this condition it swims directly into the 

 midst of a group of forms in the springing state shown in fig. 2, 

 and the utmost care is needed to keep it in view ; but as a rule not 

 many seconds ensue before it has firmly attached itself to one of the 

 springing forms, which at once unanchors itself, and both together 

 swim freely and vigorously about, as shown in fig. 12. They now 

 swim in concert for a very variable period, but generally from thirty- 

 five to forty-five minutes, when their movements become sluggish ; the 

 trailing flagella of the lower form become inert and fall upon, and be- 

 come fused with, the mass of sarcode ; meanwhile the bodies have 

 rapidly been uniting, and the two nuclei become fused together, as 

 seen in fig. 13, while the anterior flagella become, in their extremely 

 sluggish movements, at last, entangled with each other, and also melt 

 together, as shown at b, and all movement ceases. In the course of ten 

 minutes, from this condition, all trace of the separate bodies is lost, a 

 more or less regular oval form is taken, as shown in fig. 14 ; at the 

 same time a slow amoeboid disturbance of the sarcode is visible, which 

 diminishes until perfect fusion results, which occurs in the course of 

 twenty minutes, all trace of the nuclei having vanished ; and the oval 

 gradually elongates until it reaches the tight, glossy, still condition 

 shown in fig. 15. 



This, as previous experience had led me to expect, proved to be a 

 cyst charged with spores. On the first occasion, I anticipated a long 

 continuous watch ; but at the end of three hours there was a sudden 

 falling in the middle of the spindle-shaped sac, and a general altera- 

 tion of form, which led me to earnest effort to discover some discharge. 

 And that it was taking place there could be no doubt, for there was a 

 rapid diminution in the size of the sac ; and there were apparent frac- 

 tures in the delicate investing membrane ; but nothing more than 

 cloudiness at the ends could then be made out. I was using the T Vth 

 new formula lens (dry), and exhausted all expedients, in vain, to make 

 out the real cause of the change ; and as it is hopeless to attempt to 

 change a lens successfully under such circumstances, there was nothing 

 to be done but await another opportunity ; using another lens. This 

 Ytth had proved of great value throughout in the detection of minute 

 structure and change of form ; but the kind of illumination which 

 best reveals extremely minute semi-opaque bodies, is the perfect central 

 illumination which I have endeavoured to describe in the "Monthly 

 Microscopical Journal," vol. xv, page 165. That is to say, the illu- 

 mination of the whole field through a circular aperture in the dia- 

 phragm from the -gVth to the Y<ro^ n °^ an i ncn i 11 diameter, through 

 the centre of which aperture the optical axis of the sub-stage con- 

 denser, if continued, would pass. But for this special method the new 

 y^th is not so efficient in my hands as the "s^h? or g^-th. 



