442 



SCIENCE 



[N. S. Vol. XXVII. No. 690 



those of L. minima as described by Hintze 

 (1902). We find a sexual generation made 

 up of micro- and macrogametocytes with 

 corresponding gametes, a zygote resulting 

 from this conjugation, and a zygocyst with 

 from 24 to 32 sporozoites, also an asexual 

 generation arising from sporozoites and re- 

 peating itself again and again by schizo- 

 gony, in which from two to twenty mero- 

 zoites are produced. This cycle is com- 

 pleted entirely within the vertebrate host. 



We have worked out a basis of relation- 

 ship in the changes which the nucleus regu- 

 larly undergoes after each division. It 

 passes through about eight different struc- 

 tural conditions in its reconstruction, 

 whether it be during the cleavage of the 

 zygocyst, the schizont, or the gametocytes 

 or in the growth of the gametocytes and 

 schizonts. After division the nucleus is 

 either in the form of a homogeneous dense 

 karyosome, or it proceeds to assume this 

 condition. A number of spaces appear in 

 the karyosome, giving rise to a coarse net- 

 work. This network becomes a fine struc- 

 ture with enlarged nodes, the latter be- 

 coming definite chromatin bodies. The 

 network is in direct communication with 

 the nuclear membrane. In the next step, 

 both nuclear membrane and achromatic 

 network are lost and the chromatin bodies, 

 about sixteen in number, lie apparently 

 free in the cytoplasm. They become dumb- 

 bell shaped and divide, giving rise to about 

 thirty-two daughter chromatin bodies. 

 These either diminish rapidly in size, 

 while an achromatic matrix replaces them, 

 or move apart in two groups and then give 

 place to the matrix. The latter becomes 

 the karyosome of the next cycle. 



We have reason to believe there is an 

 alternation of the sexual with the asexual 

 generation in this animal. In several care- 

 fully studied cases, one generation is pres- 

 ent almost to the exclusion of the other. 

 Associated with this condition is another 



which lends support to the theory of alter- 

 nation of generations. Schizonts, micro- 

 gametoeytes, and macrogametocytes which 

 develop from merozoites that are associated 

 with zygocysts, are markedly different in 

 structure from these same types when they 

 grow from merozoites that are associated 

 with gametocytes, garnet cysts and garnets, 

 i. e., sexual stages. Moreover, the last- 

 named merozoites are produced by schizonts 

 incapable of dividing more than once or 

 twice, while the first-mentioned merozoites 

 are the progeny of very prolific schizonts. 

 It has been convenient to distinguish the 

 schizonts, microgametocytes and macro- 

 gametocytes of the prolific type as "pri- 

 mary," and the others as "secondary" 

 individuals. 



Blackhead, a Coccidial Disease of Turkeys: 

 Leon J. Cole, Yale University, and 

 Philip B. Hadley, Brown University. 



Variation, Correlation and Growth in 

 Paramecium: H. S. Jennings, Johns 

 Hopkins University. 



Sexual Reproduction in Amceia: M. M. 

 Metcalp. 



Effects of Alcohol on the Division-Rate of 



Infusoria: Lorande Loss Woodruff, 



Yale University. 



The experiments summarized were eon- 

 ducted for considerable periods on two spe- 

 cies of protozoa, Paramecium and Styl- 

 onychia, whose status in the life-cycle was 

 known through long cultures, and on a suf- 

 ficiently large number of individuals to 

 afford reliable averages. It is believed, 

 therefore, that the results obtained afford 

 clear evidence of the general effect of 

 alcohol on the division-rate and, therefore, 

 on the metabolism of the organisms 

 studied. 



The evidence thus brought forward 

 shows clearly that : 



