264 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by these processes. There is a mere flowing of the protoplasm, as in 

 Amoeba. No nucleus was to be seen, and only one specimen has been 

 observed. 



Spontaneous and Artificial Division.* — Prof. M. Nussbaum 

 describes the structure and history of Opalina ranarum and Gastro- 

 styla vorax, with special reference to spontaneous and artificial 

 division. On his results he bases a number of generalizations, and 

 adds a critical review of several recent researches on the cell. 



I. Opaliiia ranarum. (a) The division of Opalina, which seems 

 to cease during the hibernation of the frog, but which rapidly re- 

 commences if the host be warmed or fed, is effected by a cleft, which, 

 as it deepens, divides the body into two frequently unequal parts. 

 These remain slightly united by a delicate connective filament till 

 separated by a voluntary twist of the infusorian. The numerous 

 nuclei exhibit no special phenomena and no division during this 

 process, but mitosis was during other periods abundantly observed in 

 the nuclei of Opalinse of the most varied size. The structure of the 

 ciliated and encysted phases is described. (6) Nussbaum's attempts 

 to effect artificial division were unsuccessful, which was doubtless in 

 great part due to the difficulty of keeping the Opalinm alive outside 

 their host. 



II. Gastrostyla vorax. (a) In noting the habitat of this new 

 species the author lays special emphasis on the vitality of infusorian 

 cysts, which he has sometimes kept latent for two years. The struc- 

 ture of Gastrostyla, the encystation, the behaviour of "nuclei" and 

 " nucleoli," and the phenomena of division are discussed at consider- 

 able length. 



(&) In his experiments on the artificial division of this form Prof. 

 Nussbaum demonstrated the continued vitality and rapid reconstruc- 

 tion of the portions which contained nuclear substance. The portions 

 without nucleus either rapidly degenerated or persisted for a while — 

 without growth or reconstruction. 



The following generalizations are formulated and fully dis- 

 cussed by the author. (1) Nucleus and protoplasm can only live 

 in conjunction ; if isolated, death follows more or less rapidly. 

 (2) For the preservation of formative energy the nucleus is essential, 

 though Griiber has shown that certain histological differentiations 

 may not be hindered by its removal. (3) Every energy exerted by 

 the cell is indissolubly associated with a divisible substratum. In 

 this connection the author discusses the relation of polynuclear cells 

 to artificial division, the suggestive observations of Fol and others as 

 to polygastrulation, &c., and maintains that the cell represents a 

 multiple of possible individuals, which in the Protozoa are always 

 alike, though frequently different in the Metazoan cell. The subject 

 of polar globules is finally discussed, in regard to which, after an 

 investigation of fresh material, Nussbaum criticizes Van Beneden's 

 account of polar globule-formation in Ascaris, and maintains as before 

 the occurrence of ordinary nuclear division. 



* Arch. f. Mikr. Auat., xxvi. (1S8G) pp. 485-538 (4 pis.). 



