ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 425 



Flemroing has described does not take place in Ascaris ; but this subject 

 is too complicated to admit of brief summary. 



V. Origin of attractive spheres, asters, and achromatic spindle. — The 

 " attractive spheres " are to be observed in the ovum, not only during the 

 stages of " pelotonnement," but even earlier, when the pronuclei are still 

 reticulate and far separate from one another. The two appear simul- 

 taneously. They are slightly separate, and sometimes, if not always, the 

 fibrils have their central corpuscles united. Their position in relation to 

 the pronucleus seems to vary considerably in different ova. The various 

 positions and the relation to division are described. The first plane of 

 division does not represent in the Ascaris ovum the median plane of the 

 animal. The attractive spheres become more conspicuous and extensive 

 the further advanced the development of the pronuclei. It is absolutely 

 certain that the achromatic spindle is in part derived from the attractive 

 spheres. When the contours of the pronucleus are still present, those 

 rays of the spheres which are directed towards the pronucleus become 

 more apparent than all the other rays of the asters. Often they con- 

 verge, not towards the centres of the attractive spheres, but towards a 

 globule situated between the medullary and cortical zones of the spheres. 

 There appear to be two stellar centres, one for the spindle, the other for 

 the aster. 



The further history of the attractive spheres is followed in detail. The 

 doubling resulting from the division of the central corpuscles and of the 

 attractive spheres is intimately described. The spheres are permanent 

 organs of the cell, presiding over division. All the internal movements 

 which accompany cellular division have their immediate condition in the 

 contractility of the fibrils of the cellular protoplasm, which form a kind 

 of radial muscular system, composed of antagonistic groups. The central 

 corpuscle has the role of an organ of insertion. It is the first to divide, 

 and its doubling leads to the grouping of the contractile elements in two 

 systems. 



VI. The form and structure of the cell during mitosis is the subject 

 discussed in the last chapter of the memoir. (1) Subequatorial circles 

 mark on the surface of the cell the boundaries of the regions invaded by 

 the radiations of the asters. In metakinesis the cells have three portions : 

 (a) two asteroid, rounded, radiate regions, round the central corpuscles 

 of the attractive spheres, and separated medianly by the chromatic 

 equatorial plate ; and (b) a marginal ring, determining the superficial 

 formation which van Beneden calls the " bourrelet equatorial." (2) The 

 circles and polar elevations depend upon the presence of antipodal cones, 

 that is to say, on fibrillar cones where the radiations of the asters are 

 more voluminous and more active. The polar elevations are probably 

 dependent on the contractions of the fibrils of the antipodal cones. The 

 author calls attention to a recent research by Boveri, which confirms 

 some of his results. Explanation of six plates is given, but only two are 

 appended. Those are very clear, and in part semidiagrammatic. 



Polar Globules of Ascaris.* — Herr T. Boveri has made some im- 

 portant contributions to the investigation of the processes of maturation 

 in the ovum of Ascaris. Van Beneden's prophecy has been indeed 

 fulfilled, for the eggs of these Nematodes have become zoologically 



* Biol. Ceutralbl., viii. (1888) pp. 17-9. Zellen-Studien, Jena, 1887, 4 pis. 



