762 MICKOSCOPIC FORMS OF ANIMAL LIFE 



saprophytic organism l of special character, have been discovered 

 during a recent period. But it will be of more moment here to note 

 to what an extent in this series of observations the neiv homo</<'ii<'<>n* 

 objectives, espe-cialli/ in tin 1 if apochromatic form, have been success- 

 fully employed in enlarging the area of knowledge. 



The present Editor has gone carefully over the greater part of the 

 work, revising all the critical points with the best apochromatic ob- 

 jectives, and the homogeneous forms of achroinatics with an aperture 

 of 1'50 and with a clear demonstration of the immensely greater ease 

 with which the work could have been done had these lenses been used 

 in the original investigation. 



But the easily accessible proof of this is given in the work done by 

 Dr. Dallinger upon the nucleus of the nucleated forms of these monads. 



Briefly to present the facts, we may recall the part taken in the 

 act of fission in the form last described (Dallingeria Drysdali). It 

 will be seen by reference that it appeared to us that the nt'-clrtis fol- 

 lowed the processes inaugurated !>;/ the somatic sarcode. That in fact 

 it was a passive participator in the act of fission. This is all that 

 can be made out to-day by the very lenses originally employed. 



But by the employment of a ^Vth inch and Troth inch homo- 

 geneous of N.A. 1-50 by Powell and Lealaiid, and an apochromatic 

 of T Vth inch N.A. 1'40 by the same firm ; and also by the use of 

 the beautiful 3 mm. and 2 mm. N.A. T40 of Zeiss (apochromatic), 

 it can be seen with comparative ease that it is in the nucleus that 

 all the activities of the body are originated. 



This may be followed from a study of Plate XVI. Fig. 1, A, 

 represents the nucleus of the form drawn at fig. i, E, Plate 

 XV. In long diameter it is of an average length of siro-ooth f :m 

 inch ; but instead of being a darkly refractive object, as seen with 

 the objectives used twelve years ago, it is with the present lenses, 

 freed from chromatic and spherical aberration, a body in the monad 

 undergoing no process of change, an oval globule with a complicated 

 plexus-like involution throughout its substance, as seen in fig. (>. A. 

 Plate XVI. But directly the process of fission is to be inaugurated, 

 we need not wait to see its first action in the splitting of the 

 fiagellnm, as in fig. -2, E, Plate XV ; for by observing the nucleus 

 we discover, before any change has begun in the body-substance, 

 that the plexus in the nucleus has condensed itself 011 either side of 

 the nucleus, as in fig. 1, b, A, Plate XVI. A clear space is left at c, 

 and no change has taken place in the bodv-sarcode, a, a, a. But 

 shortly an incision takes place in the nucleus, as at d, fig. 2, and 

 this is immediately followed by the incision f in the body-sarcode, 

 and the process goes 011 simultaneously in nucleus and body, as in 

 fig. 3, until the division of the nucleus is completely effected, and the 

 total severance of the body follows. 



But as soon as the nucleus is divided, the plexus, which has been 

 during division, as in fig. 3, condensed over part of each dividing 

 half, at once distributes itself evenly again, as in fig. 6, A, and re- 

 mains so until another change is inaugurated in the form to which 

 the nucleus belongs. 



1 Jo urn. of lioi/al Micros. Soc. vol. v. 



