HARDWICKE'S SCIENCE-GOSSIP. 



und die Vererbung, eine Kritik der Weismann- 

 'schen Theorie von der Kontinuitrit des Keitn- 

 plasma," in " Zeit. fiir wiss. Zool." xliv. 1886 ; 

 Flemming in " Arch. f. mikrosk. Anat." vol. xvi.- 

 3vx. ; Strasburger's " Ueber ein. z. Demonstration 

 geeignetes Zelltheilungs-Object," in " Sitz. d. 

 Jenaischen Gesell. f. Med. u. Naturwiss.," July 18, 

 1879, and "Zellbildung und Zelltheilung," i88o ; 

 Drasch, "Wiener Sitzungsber.," 1881 ; Klein in 



i)'ig. 126. — Diagram showing the mode of nuclear division. 

 A shows strongly marked chromatin filaments with the 

 spindle figure. At the ends or points of the figure observe 

 the star-shaped or radiating arrangement of the protoplasm, 

 and in the middle of the spindle the chromatin filaments. In 

 the latter a longitudinal division of the filaments has already- 

 begun. B shows the number of chromatin filaments multi- 

 plied by division and beginning to be arranged wiih the loops 

 in the same direction as the spindle ; c shows the loops still 

 smore regularly arranged ; D, both groups of the filaments or 

 loops have retreated towards the poles of the spindle (after 

 Rabl). 



" Quart. Journ. Micr. Science," 1878 and 1879 ; 

 Eberth in " Virch. Arch." vol. 67 ; and Arnold in 

 "' Virch. Arch." vols. 77 and 78. 



Has the extrusion of the polar bodies anything to 

 ■do with these karyokinetic changes? Flemming 

 virorking in 1882 came to the opinion that the 

 phenomena in both are identical, except that in the 

 ovum the achromatin element is predominant, and 

 that therefore it is in the achromatin figures which 

 principally are fixed upon our attention. Van 



E"icr. 127. — Young egg of Flolotkuria Bohadschia; m, the 

 opening ol the micrupyle (after Semper). 



Beneden in Ascaris vic^alocephala has observed the 

 production of a Y-shaped figure which he has 

 called the ypsiliform-figure, but as this has not been 

 observed as yet in the MoUusca I accord to it here 

 but a passing notice. 



One spermatozoon is all that is necessary for the 

 foundation of the ovum. The spermatozoon enters by 

 an aperture termed the micropyle ; its tail becomes 

 absorbed, and the head remains to form the male 

 pronucleus. According to Van Beneden and Blom- 

 field,* the spermatozoon throws off a body (seminal 

 granule) previous to fecundation and while it is 

 within the ovum, probably with the second polar 

 body ; after the extrusion of the second polar body, 

 the remaining portion of the germinal vesicle is 

 termed the "female pronucleus." Fecundation con- 

 sists in the fusion of the male and female pronuclei. 

 For the discussion as to the consideration of re- 

 garding each living cell as a distinct hermaphrodite 

 being, I must ask the reader to refer to the papers of 

 Professor Sedgewick, Minot, since it is of too lengthy 

 a character to discuss here, and a mention of the 

 fact only suffices my purpose in this relation. He 

 will find the papers in the fourth volume of 

 " Science " for 1884, and in the "Proceedings of the 

 Boston Society of Natural History " for 1887. After 

 the union of the male and female pronuclei the ovum 

 passes through the changes described on pp. 43 and 

 44 of my book "Land and Fresh- water Shells," in 

 the " Young Collector Series," to which I must also 

 ask the reader to refer. Every cell-division that the 

 ovum undergoes, the reader will remember, is pre- 

 ceded by karyokinetic changes in the nucleus. 



Thus I have massed here together in as small a 

 space as possible the material on which I shall found 

 the subject of Part IV. — The Probable Cause of 

 Variation. 



NOTE ON A TURBELLARIAN WORM. 



EXAMINING some decaying leaves of cerato- 

 phyllum the other day, I disturbed a fine 

 specimen of a turbellarian worm. He was favour- 

 ably situated for drawing, being fixed in a clear 

 space in the debris of the dead leaves, where he 

 would not move freely, and where he seemed to 

 realize the position, keeping as quiet as it is possible 

 for one of these active, restless worms to remain. 

 I have killed them with osmic acid, but the results 

 have always been unsatisfactory, the animal con- 

 tracting, &c. In this instance no osmic acid was 

 used. The entire surface of the body was coated 

 with cilia, and with careful illumination these could 

 be seen in motion, not only on the edges, but also 

 over the body (Fig. 12S). The oral aperture, o, was 

 ventral, and placed immediately above a strong 

 muscular organ, /, the pharynx ; the lips of the 

 mouth were fringed with cilia, which seemed to 

 extend into its interior. The stomach, s, was large, 

 and of a yellowish colour ; but I coidd not detect 



* Van Beneden, "La Spermatogenese chez I'Ascaride mega- 

 loccphale,'' "Bull, de I'Acade'mie Royale de Belgique," 1884; 

 Blomfield, " The Development of the Spermatozoa," Q. J. M. S. 

 1800. - ._ 



