926 SUMMARY OF CUIIUENT RESEARCHES RELATING TO 



polo. The very young ova had the usual round form ; the elongated 

 shape was assumed aloug with the granulation of the vitellus. The 

 ovarian ova are more minutely described. In regard to the origin of the 

 blastoderm Kupflfer's observations arc confirmed. The incubation lasts 

 2-3 days ; the larvro are like those of other Clupeids ; the vitellus is 

 prolonged far back in the abdominal cavity, and the yolk-sac lias a much 

 restricted and elongated form. The very large notochord, the transverse 

 folding of the post-pyloric portion of the intestine, are then alluded to. 

 Referring to his previous dcscrii)tion of Clupea pilchardus, the author 

 a^ain cmidiasizcs the vesicular structure of the vitellus as expressing a 

 natural aflBuity. 



Heredity.* — Prof. A. Weismann discusses the alleged botanical 

 evidence in favour of the inheritance of acquired characters. In a pre- 

 liminary discussion the author reiterates the essentials of his often 

 misunderstood position. Individually acquired characteristics, not of 

 constitutional origin, are not transmitted ; functional and environmental 

 variations may cflfeet the "soma" of the individual, but unless the repro- 

 ductive elements be affected there can be no transmission ; proof of the 

 transmission of such variations is not forthcoming ; the ground is taken 

 from under the feet of Lamarckians ; direct germinal modification 

 remains the sole fountain of specific variation. But Detmer and Hoff- 

 mann have submitted a number of cases among plants which appeared 

 to these botanists to warrant the conclusion that individually acquired 

 characters might be transmitted. Weismann subjects Detmer's cases to 

 examination, but does not find that any of them warrant the conclu- 

 sion drawn. All the illustrations given by Hoffmann arc secondary 

 variations in consequence of variations in the germinal protoplasm, none 

 of them are directly acquired modifications of the soma. With the 

 former, Weismann has of course no difficulty. Beyond the critique of 

 the two botanical memoirs, the paper contains numerous side-remarks 

 illustrating the author's position. 



Principle of Heredity and the Laws of Mechanics applied to the 

 Morphology of Solitary Cells.! — M. M. W. Khawkine has made a study 

 of the develoi)meut of Paramsecium aurelia. He observes that a mother- 

 cell of Paramsecium, in which fission is produced, has an annular constric- 

 tion but no other depression of the body ; on the contrary, its external 

 layer is stretched, its contours are rounded, and the whole of its body 

 approaches the form of a revolving solid. The young organisms when 

 freshly separated have likewise no depression, and approach the same 

 form. Under ordinary conditions the freshly separated Paramaecia long 

 remain at the same place, working with the cilia of their ventral surface 

 so as to attract food ; or the young Paramsecium may at once begin to 

 swim and turn somersaults in the surrounding water ; as this somersault 

 and movement of rotation are always produced in opposite directions, 

 the work is almost exclusively that of the ventral cilia. It is possible 

 that it is the large share in diffusion which obtains in the region of the 

 mouth that is the direct cause of the greater part of the work being 

 thrown on the ventral cilia, and of their elongation and increase in 

 strength ; whatever and however it be, the work of these cilia produces 

 a pressure on the whole of the corresponding surface of the body. This 



» Biol. Centralbl., viii. (1888) pp. 65-79, 98-1 (i9. 

 t Arch. Zool. Exper. tt Gen., vi. (1888) pp. 1-20. 



