ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 259 



tho lower end of the small intestine of a frog, and drawing out a little 

 of the contents of the large intestine, placed them carefully in water 

 on a slide ; with a pair of fine forceps all visible particles were 

 removed, and then a quite thin but not too small cover-glass was laid 

 on. If the drop as spread out be thin enough, the large Opaline 

 contained in the gut will be flattened out. As soon as satisfactory 

 examples have been detected a margin of concentrated picric acid 

 solution must be run round with a brush ; when (after some days) 

 this has passed beneath the cover-glass, the preparation is carefully 

 washed until the Opalinse, which will now be visible to the naked 

 eye, are quite colourless. After a repetition of the washing, a 

 very strong solution of alum-carmine must be used like the picric 

 acid, and the slide again placed in the moist chamber ; after some 

 days (or if fresh htematoxylin be used instead, after some hours), the 

 superfluous colouring matter is to be washed away. Pure absolute 

 alcohol is then sucked through the preparation, and then a ring is 

 made of oil of cloves. After a short time the alcohol evaporates, and 

 the oil of cloves takes its place. If it be desired to preserve the 

 preparation, which is otherwise now ready, xylol is used after the oil 

 of cloves, and then a very thin solution of Canada balsam in xylol is 

 allowed to enter. 



In such a preparation the chromatin and the nucleoli will be found 

 to be coloured, and all the rest colourless ; the cilia are extended and 

 well preserved, and there are no indications of any solution of con- 

 tinuity or shrinking of the cell-body. A series of forms must be 

 studied and compared. 



The resting nucleus exhibits the three constituents — chromatin, 

 prochromatin, and achromatin, the parachromatin being obscured ; 

 the chromatin is in the form of a fine irregular plexus of fibres of 

 varying thickness ; the marginal layer is the most prominent, but 

 there is a membrane composed of thicker portions of filaments ; the 

 greater part of the nucleus is very poor in chromatin ; there are 

 generally a number of relatively large nucleoli, which are sometimes 

 arranged in a manner strikingly like those of the mature frog's 

 ovum. 



The commencement of kinesis is indicated by the formation of a 

 coil of filaments of equal thickness ; at first very finely filamentar 

 and closely meshed, the filaments become thicker later on, the coils 

 looser, and the whole extends beyond the limits of the nucleus. 

 Segmentation then commences ; the filaments shorten and thicken, 

 and a central plate is formed. About this time the filaments are cleft 

 longitudinally. 



Metakinesis now ensues ; the segments undergo such a rearrange- 

 ment that the free ends lie towards the equator, and the convex sides 

 towards the poles ; it is not certain whether this change is directly 

 connected with the longitudinal cleavage. The two segment-com- 

 plexes, which result from the metakinesis, separate from one another, 

 and gradually consolidate. The ground-substance of the nucleus 

 exhibits a very interesting character, the chief point in which is that 

 it becomes sharply separated from the cell-body. The resting nucleus 



S 2 



