March 3, 1899.] 



SCIENCE. 



!19 



chanics of diiferentiation. Of the four 

 common]}' recognized features of differen- 

 tial cleavage — viz.: (1) inequality, (2) non- 

 alternation of directions, (3) qualitative dif- 

 ferentiation and (4) lack of rhythm — the 

 first three may be correlated with these 

 movements. Unequal cleavages are due to 

 movements which, beginning with the earlj^ 

 anaphase, carry the nucleus out of the center 

 of the cell. Non-alternation is due to the 

 absence of currents, alternation to the regu- 

 lar reversal of currents during each succes- 

 sive division. Certain qualitative differences 

 of the two daughter cells of every cleavage 

 are also due to these movements. The re- 

 mains of the centrosphere (idiosome of 

 Meves, mother periplast of Vejdovski) in 

 each blastomere is carried by definite rota- 

 tions of the protoplasm into one only of the 

 two daughter cells into which the blasto- 

 mere divides ; there is thus produced by 

 protoplastic movement a visible qualitative 

 difference in the two daughter cells formed 

 at every division. 



The Characteristics of Mitosis and Amitosis. S. 

 Watase. 



On Hcematococcus . F. H. Herrick. 



Observations on Htematococcus began 

 with Girod-Chantrans in 1797 and have 

 been continued during the present century 

 by Agardh, Colin, Braun, Rostafinski, 

 Biitschli and others. The chief points of 

 contention lie in the supposed sexual char- 

 acter of this organism and in the structure 

 and functions of the zoospores. 



The following summary of results was 

 presented : (1) Resting cells after long sub- 

 mergence in water lose the power of devel- 

 opment. In one case, after being submerged 

 for two years, the cells have greatly thick- 

 ened walls, but no zoospores are formed. If 

 these cells are now dried, even for a short 

 time, and then returned to water develop- 

 ment rapidly follows. Htematococcus has 

 thus become adapted to the alternation of 



drought and moisture, so that desiccation or 

 something equivalent to this has become 

 necessary to bring about a normal response. 

 (2) Great variation not only occurs in the 

 form and size of the sporangium (developing 

 mother cell wall) and in the number of the 

 zoospores, but in the size of the zoospores 

 produced in the same sporangium. In re- 

 spect to size at least the terms ' macrozoo- 

 spore ' and ' microzoospore ' have no signifi- 

 cance. (3) The zoospores imbibe water 

 after liberation and undergo marked changes 

 in appearance. Before maintaining that all 

 zoospores have a similar structure, it may 

 be necessary to repeat and extend certain 

 experiments, but we are convinced that no 

 sexuality can be attributed to this form, and 

 that no true copulation has ever been ob- 

 served. (4) Monstrosities frequently occur 

 in the motile stage, such as twins and cells 

 with four or more ' heads ' (pairs of flagella) 

 in all cases due not to fusion, but to incom- 

 plete division of the mother cell. (5) Re- 

 production by internal cell division has 

 been observed in the motile stage in a few 

 cases, in one of which the zoospore-colon}' 

 consisted of four small cells freely moving 

 in the sac of the mother zoospore, which was 

 itself distinctly propelled by its own cilia. 

 The mother capsule soon burst setting the 

 young free. (6) When a motile cell comes 

 to rest its protoplasmic sac contracts and a 

 spherical resting cell is formed which secretes 

 its proper wall while still enclosed in the 

 evanescent wall of the zoospore. The flagella 

 break at the 'beak,' leaving two slender 

 rods united with the wall of the metamor- 

 phosed zoospore. These are probably elastic 

 cellulose tubes which serve to sustain the 

 flagella at the points where they pierce the 

 sac. (7) In the course of zoospore-forma- 

 tion in large cells endosmosis is very great 

 and the surface tension of the wall unequal. 

 The transparent sphere is blown out in a 

 form often resembling that of an incandes- 

 cent light bulb, with abundant room for the 



