398 Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



than the central dense massing of the rays of the aster; and may 

 vary from a dense spherical mass to a ring of circular or oval shape, 

 which latter may be so drawn out as to be almost linear in form. 

 The astrospheres are usually two in number, but there may be 

 three or even four, produced very likely by the overlapping of the 

 rays at one or two points on the equator of the spindle. That the 

 cytoplasm of the egg is subjected to considerable centrifugal 

 force during mitosis is evidenced by the massing of the yolk in 

 an out er equatorial zone. The equatorial plate forms directly 

 from the nuclear reticulum, with no precedent skein stage, the 

 chromatin gathering itself together, apparently under the in- 

 fluence of the asters, into -a varying number (ranging at least 

 from three to ten) of irregulär chromosomes. Occasionally an 

 early anaphase is found, but a telophase I have never seen in the 

 numerous cases of maturation studied by me. While the asters 

 are the first to form, they are likewise the first to disappear, in- 

 stances having been observed in which the chromosomes were 

 still in the equatorial plate while the astral figure was degener ating. 

 I have hunted long and carefully for polar bodies but have been 

 unable to find them in any case. 



I have not as yet made a detailed study of the adult cestode 

 spermatozoan, but its structure apparently agrees with the de- 

 scriptions of previous authors, according to which it consists merely 

 of a filament, without distinctly differentiated head, neck or tail. 

 After entering the egg the entering end enlarges and soon breaks 

 up into several chromosomes, the number of which I have not 

 ascertained, but which is probably variable. 



At this stage cleavage ensues either with or without the 

 formation of a fusion nucleus. In the former case nuclear division 

 is typically amitotic, tho in later stages of cleavage many in- 

 stances of mitosis have been found. In the latter case the chromo- 

 somes of (5 and 9 pronuclei gradually separate from one another, 

 surrounding themselves mean while with membranes; while other 

 cleavage nuclei may arise de novo in the cytoplasm of the egg, 

 similarly to the manner above described in the later stages of 

 larva and adult. 



Most of the eggs in the uterus have attached to them a yolk 

 cell, whose yolk is soon lost, apparently being surrendered to the 

 egg by a process of digestion and absorption. The actual moment 

 of attachment of this cell has not, so far as I know been observed, 

 and very different interpretations have been given by various 

 authors to what is apparently the same cell in different species. 

 The ,, polar body" of Child (1907 a, b, c, d), the „cellule granu- 

 leuse" of St. Remy (1901), and the yolk cell of Leuckart 1 ) 



') Fide v. Janicki (1907). 



