658 



SCIENCE 



[N. S. VoL.XLII. No. 1088 



Drawings for Monograph on Pacific Tintin- 

 noidea, C. A. Kofoid and Mrs. Elizabeth Puring- 

 ton, University of California. 



Balantidium from the Pig, J. D. MacDonald, 

 University of California. 



Drawings of ElasmobranehSj J. Prank Daniels, 

 University of California. 



Papers: Protozoology 

 Chakles a. KoroiD, University of California, 



presiding 

 Chromosomes in Protozoa: Maynaed M. Metcalf, 



Oberlin, Ohio. 



This review has endeavored to show that in each 

 group of the Protozoa are found elongated 

 chromosomes which are linear aggregates of gran- 

 ules and which split longitudinally in mitosis, giv- 

 ing exact equivalence of the daughter nuclei. In 

 all major groups, except perhaps the Mastigo- 

 phora, presexual and sexual phenomena, essentially 

 similar to those of Metasoa are known. The Meta- 

 zoan mechanism of inheritance is therefore pres- 

 ent, in some representatives at least, of all the 

 great Protozoan groups. It has shown also that, 

 in some representatives, at least, of the Plasmo- 

 drome, during the vegetative phases of the life his- 

 tory, the chromatin outside the earyosome, indeed 

 apparently outside the caryoli, is thrown off as 

 trophieal chromidia. Such evolution of complex- 

 ity of organization as has occurred in the Metasoa 

 probably could not occur until, as in the Ciliata, a 

 considerable amount of chromatin is kept intact 

 throughout the whole life history, including its 

 vegetative as well as its presexual and sexual 

 phases. The lower Protozoa have the Metazoan 

 type of mechanism of inheritance in connection 

 with their sexual phases but can not utilize it for 

 the development of a complex series of determin- 

 ers for elaborate structural organization, for they 

 do not keep this mechanism intact during their 

 vegetative periods. The higher Protozoa appar- 

 ently have the Metazoan type of mechanism of in- 

 heritance and keep it intact through all their life 

 cycle. To what extent they have utilized its pres- 

 ence to develop determiners, is an interesting ques- 

 tion which does not seem beyond experimental 

 study with favorable material. 



Problems on Pejuvenescence in Protozoa (illus- 

 trated with lantern slides) : Loeande L. Wood- 

 ruff, Yale University (read by title). 



The Evolution of the Protozoan Nucleus and Its 

 Extranuclear Connections: Chakles Atwood 

 KOPOID, University of California. 



The essential and fundamental similarity of 

 Protozoan and metazoan nucleus is indicated by 

 the general trend of recent cytological investiga- 

 tions among the Protozoa. The process of mitosis 

 has the same sequence of phases, though the 

 chronology of mitotic events and of the division 

 of extranuclear structures varies from species to 

 species and also among individuals within the spe- 

 cies. In the early prophase in trichomonad flagel- 

 lates and in Nwgleria the chromatin aggregates, 

 presumably chromosomes each split longitudinally, 

 or the chromatin network forms a split skein or 

 thread which later fuses into one, or emerges on 

 the equatorial plate in chromosomes in which the 

 precocious splitting has entirely disappeared. The 

 chromosomes are definite in number and are dif- 

 ferentiated among themselves as to size and be- 

 havior in mitosis. There are suggestions of odd 

 and even numbers (4, 5) there is (in Trichomonad 

 flagellates in several genera and species) a small 

 chromosome lagging in the metaphase, and there 

 are instances of unequal division of chromosomes. 



The blepharoplast contains the centrosome in 

 trichomonad flagellates or is attached to it 

 (Giardia-Lamblia) . This organelle should not be 

 called a kinetonucleus; Schaudinn's report of its 

 heteropole origin by mitosis is unsupported and 

 probably invalid. It arises in enflagellating 

 Ncegleria {-Amceba) griiberi from the centrosome 

 or centriole in the central earyosome, which sends 

 out a radial fibril which enlarges at the periphery 

 into a blepharoplast at the base of the two 

 flagellaj which grow out from this enlargement. 

 In exflagellation the flagella withdraw and to- 

 gether with the blepharoplast retreat into the 

 earyosome. The blepharoplast is highly developed 

 in parasitic flagellates and is directly connected 

 by a system of fibrils with nucleus, flagella, axo- 

 style and parabasal body, the whole forming an 

 integrated structural unit which functions as a 

 neuromotor apparatus comparable with that of 

 the ciliate Diplodinium. It is a specialized struc- 

 ture developed to the greatest extent in connec- 

 tion with parasitic life demanding unusual ex- 

 penditure of energy in locomotor activity. The 

 term kinetonucleus should be abandoned as mis- 

 leading. The Biauclearity Hypothesis in its nu- 

 clear implications has no adequate foundations, 

 and the order Binucleata should be discajded. 

 The parabasal body of flagellates and Trichony- 

 phida is perhaps the analogue of the maoronucleus 

 of the eiliates and is an extranuclear store of the 

 chromatin related to the needs of flagellar and 

 ciliary activities. 



