and Laboratory Methods. 1337 



In the division of the periplast cells of Selachians two types are recognizable, 

 one in which the nuclei have central, regularly arranged chromatin, and another 

 in which the chromatin is rod-shaped in separate pieces. Those of the first type 

 are found earlier in development. The nuclei contain several small granules to 

 which small furrows run radially. These granules grow to large masses without 

 loosing their relations to the radial grooves. Later a giant cell contains six, 

 eight or more large nucleoli. The nuclei of the second type with separate 

 chromatin rods are distinguished by their transparency and even staining. 

 Transition forms are found forming two lines, one in the direction of dissocia- 

 tion and one towards synthesis. The former process is a simple breaking up 

 of the chromatin rods into fine granules. Many stages of these are found. 

 Reconstructive processes follow definite steps : (1) Breaking up of the plasma 

 bodies, carrying the chromatin into several small balls ; (2) separation of these 

 balls, still remaining connected by a thread ; (3) re-appearance of chromatic 

 rods ; (4) radial structure appears in connection with chromatin ; (5) formation 

 of enclosed nuclei, thickening of nuclear wall. The process continued still 

 farther and showed itself that of a syncytial formation ; it is a kind of nuclear 

 division. Comparing this process with regular bipolar mitosis, we find in com- 

 mon the phases of dissociation of chromatin — prophases ; the formation of the 

 chromatin rods and their radial arrangement are the anaphases. The meta- 

 phase would correspond to the dissociated mass of granules. As long as the 

 plasma of the nucleus retains a connection with the dissociated chromatin a 

 " spirem " is present. The equivalent of spindle fibers are the plasma threads 

 stretched between the nuclear balls. The origin and relations of polycentric 

 giant cells are understandable on general cellular laws. It is known that a 

 central force acts in such phenomena as division. Its nature is unknown, but 

 simple exhibitions of " pull " and " push " are to be seen. 



The process of mitosis can be divided into five steps : (1) The division of 

 the pre-existing centrosome ; (2) the separation of these parts ; (3) the changed 

 influence of these centrosomes, due to their changed position, shown in the 

 appearance of double radiations ; (4) the grouping of the chromatin bodies 

 and arrangement in the daughter nucleus ; (5) the formation of cell walls. 

 Each of these processes requires a separate time ; but any change in the time 

 requisite for these steps may change the appearances entirely. If the division 

 of centrosomes is relatively too rapid, new ones arise without the correlated 

 changes, and the subsequent steps are those of cells with many centrosomes. 

 The distribution of the chromatin is, hence, difficult to follow. The relation of 

 the nucleolus to these centrosomes and the plasma cells remains yet to be 

 studied. a. m. c. 



Moll, A. Zur Histochemie der Korpels. From the results of the author. Tan zer's 



Centralbl. f. Physiol. 13 : 2215-226,1800. . ... , • ak ^i^^i^^i 



■' 3 ' yy orcein solution (orcein 0.5 gram, alcohol 



absolute 40.0 c. c, dist. water 20.0 c. c, hydrochloric acid 10 drops) is an instructive 



double stain for embryonic cartilage. The preparations (embryos or parts of 



them) must be hardened in alcohol (not in chromic acid), and then in thin 



celloidin sections be put into the above staining solution for 6-24 hours, then 



washed in 80 or 90 per cent, alcohol until the celloidin is nearly colorless. 



