8 NATURAL SCIENCE. Jan, 



to bring forward shortly. Besides many interesting details concern- 

 ing the structure of the protoplasm and shell of Diatoms, and some 

 valuable methods of staining the tissue while living, important and 

 striking results were obtained with regard to the nuclear division, which 

 in these forms always takes place by karyokinesis. The centrosome is 

 always present close beside the nucleus, and visible even during life in 

 the resting cell, but there are no striations round it until the commence- 

 ment of division. At an early stage in the division there appears, 

 between the centrosome and nucleus, a third body, which is the 

 rudiment (Anlage) of the central spindle — though never spindle- 

 shaped itself. It is probably derived from the centrosome, perhaps 

 by division, but its origin has not been clearly made out. Appearing 

 originally as a rounded body, then becoming rod-shaped, it expands 

 and grows in a peculiar manner, which may best be illustrated by 

 comparing its shape first to a coin, then, by increase of depth, to a 

 piece used in the game of draughts, then to a drum, and, finally, to 

 an elongated cylinder, which is longitudinally striated. Hence, 

 in the rod-like stage its long axis does not correspond to the long 

 axis of the future spindle, but to its transverse axis. When full- 

 grown, it sinks into the nucleus, which, in the meanwhile, has passed 

 through the stages with the dense and loose skein, and has 

 now lost its membrane, and contains V-shaped chromosomes. 

 At this period the centrosome, with its system of rays, becomes 

 indistinct and disappears, and the cell protoplasm shows radiate 

 striations round each of the poles of the central spindle. The chromo- 

 somes form an equatorial ring round the central spindle {Monaster 

 stage). The ring splits into two rings which travel apart {Dyastev 

 stage). The two rings become narrowed and constrict off the two. 

 ends of the central spindle, the two pieces so cut off becoming the 

 centrosomes of the daughter cells. The cleavage of the cell passes 

 through the middle of the central spindle, halving it accurately. The 

 two halves of the central spindle perhaps become absorbed into the 

 pieces which were cut off to form the daughter centrosomes. The 

 daughter nuclei reconstitute themselves. The author concludes his 

 paper with some interesting comparisons between this peculiar mode 

 of formation of the nuclear spindle in Diatoms and in other cells. 

 He considers that his observations support Biitschh's view of the 

 homology between the centrosome and the micro-nucleus of Infusoria. 

 It is interesting to note that all the stages of karyokinesis described 

 — and observed chiefly in Snrviella calcavata, Pfitzer, but confirmed in 

 other species — were seen and drawn in the living state as well as in 

 preparations ; also that the protoplasm of these forms shows, both 

 when living and after fixation, a distinct reticulate alveolar meshwork. 

 The striations round the centrosome are seen to be formed by arrange- 

 ment of the meshes or alveoli in rows, as formerly described by 

 Biitschli. Dr. Lauterborn's complete work will be awaited with 

 considerable interest. 



