Royal Microscopical Society. 265 



power of from 1200 to 10,000 diameters, the fine hyaline invest- 

 ment in the initial stages of development is perceived more clearly, 

 enveloping the monad, but no change of shape or motion ensues, 

 Fig. 4. In about forty minutes to an hour a hne suddenly appears 

 across the short diameter of the oval, which soon develops into a 

 very marked constriction, as seen in Fig. 5. This constriction 

 continues rapidly to increase within the hyaline membrane, which 

 throughout the process preserves its normal form, until it reaches 

 the condition drawn in Fig. 6. During the whole of this time the 

 motion of the monad is unaffected ; and in about two hours from 

 the first* a total division takes place. Just before division, however, 

 in some way not made out, two short ciha appear in the place of the 

 future flagella, as seen in a. Fig. 6 ; but directly actual division takes 

 place the separated monad turns over, and occupies the position 

 seen in a. Fig. 7. After swimming freely in this condition for not 

 less than ten minutes an indentation may be observed in the long 

 axis of the divided bodies within the hyaline, and in from seven to 

 twenty minutes a constriction longwise ensues,t as seen in Fig. 8, 

 where a and h show the lines of constriction. After this the divided 

 bodies remain within the hyaline envelope, sometimes dividing into 

 eight and even into sixteen, although rarely, and swim about with 

 an elegance and ease certainly not surpassed by the pregnant Volvox 

 globator. Generally this compound mass is dependent for motion 

 on the original flagella of the original monad, which persist through- 

 out ; but at times, determined by conditions we have not discovered, 

 the flagella of each new form protrude beyond the hyaline envelope, 

 as seen in Fig. 9, but these always move in concert, and apparently 

 obey a common impulse. After swimming in this way for a length 

 of time, varying from ten to one hundred minutes, or more, one of 

 the forms within the hyaline investment protrudes itself, as seen in 

 Fig. 10, and shortly escapes a perfect monad like its parent. This 

 is repeated in each case until in the majority of instances all escape, 

 leaving the fragment of a pellicle or sac behind with the old flagella 

 attached, as drawn in Fig. 11. But in many cases there appears to 

 be incapacity to throw ofi" the last one or two, and it remains 

 apparently dead, as seen in Fig. 12. This is the usual method 

 of increase, and goes on with great rapidity ; the multiple forms 

 in a fresh field, always bearing a large proportion to the other 

 forms. This process does not terminate with the first generation 

 so produced, but may be continued for many generations in 

 succession with no congress of any kind and no visible modifica- 

 tions. 



(2.) But the attentive and patient observer will soon find 



* Sometimes it is much quicker, and at otlier times much slower than this, 

 t This is not invariable : sometimes the constrictions are all along the short 

 diameter. 



