Royal Microscopical Society. 69 



II,— Further Besearches into the Life History of the Monads. 

 By W. H. Dallinger, F.R.M.S., and J. Drysdale, M.D. 



(Read before the Eoyal Microscopical Society, Jan. 7, 1874.) 



Plate LII. and upper part of LI. 



We now proceed to describe the development of the last of the 

 monads included in the present series of researches. 



Its exterior form is extremely simple, being ovoid with a single 

 flagellum. In long diameter it never exceeds the ToVo^ti of an inch, 

 and in a great number of cases was not greater than the qr^'oTyth. 

 Its general appearance is shown by Fig. 1, PI. LII. The sarcode 

 is somewhat whiter than in the others we have described, and it is 

 much freer from vacuoles. No definite body answering to a nucleus 

 could be made out at any stage of development, but the morpho- 

 logical cycle has points strikingly kindred with those before de- 

 scribed, and at the same time points remarkably divergent. 



Its mode of locomotion differs from the other forms we have 

 described in being quite uniform — a slow straight motion, without 

 jerking or irregularity. In the younger forms the flagellum was 

 motile as usual from end to end ; but in the older forms there was 

 a greater or less thickening of the flagellum at the end attached 

 to the body, and this in many cases became extremely marked; 

 assuming, finally, a rigid condition for about a fourth of its length, 

 as may be seen in the drawing, Fig. 19, PI. LI., upper portion. 



The rapidity and copiousness of its multiplication was remarked 

 by us at a very early stage of our investigations. Multitudes of 

 adult forms in a very short time — a time entirely too short for their 

 development from sporules, if our former experiences were to guide 

 us — swarmed the field. But this was subsequently explained by 

 their remarkable mode of multiple fission. The process was simple 

 and rapid. 



The first indication that it was about to happen was given by the 

 monad assuming a rounder form, sometimes as in Fig. 2, PI. LII., 

 shghtly flattened, giving an appearance approximating to a spht pea. 

 This might continue for twenty or thirty minutes, the monad swim- 

 ming freely and gracefully as before the change occurred. After this 

 it became slightly amoeboid and somewhat uncertain in form ; Fig. 3 

 represents it as frequently seen in this stage, which was one of great 

 activity, but only lasted from four to ten minutes, when an actually 

 globular form was taken and the creature became still ; the flagellum 

 moved sluggishly for a very few minutes and then disappeared. Its 

 appearance is drawn in Fig. 4. If now the httle globe were care- 

 fully watched with a magnification of about 3000 diameters, there 

 would appear, per saltum, a white cruciform mark — evidently a 



