424 SUMMARY OF CURRENT RESEARCHES RELATING TO 



II. Preliminary Kinesis. — The pronuclei do not conjugate. Tho 

 formation in each of a chromatic band (cordon) is intimately described. 

 It resolves itself into two primary chromatic loops. Tho pronuclei are 

 directed laterally to one another, with their polar regions towards the 

 attractive spheres between them. At length the chromatic loops of tho 

 two groups come to lie indistinguishably side by side. They then form 

 secondary loops by longitudinal division. The primary chromatic stars 

 divide into two secondary chromatic stare, which separate. The order of 

 priority as regards tho longitudinal division of the primary loops is 

 (1) Van Bencden ; (2) a month later, Hensen ; (3) several months later, 

 liabl. There is no fusion of pronuclei ; the chromatin elements of malo 

 and female pronucleus furnish each two chromatic loops to the nuclei of 

 the two first blastomeres ; the same process always occurs ; transmission 

 is effected, therefore, by the chromatic distribution. 



III. Theory of Fertilization. — It is evident that the facts of fertiliza- 

 tion, according to Van Beneden, are not exactly harmonious with Hertwig's 

 theory of fertilization. The nuclear fusion so important for the latter is 

 not recognized by the former. (1) The genesis of the pronuclei coin- 

 cides exactly with the elimination of the second polar globule, i. e. with 

 the completed maturation of the ovum. (2) In the vast majority of cases 

 the pronuclei do not even become adjacent. (3) The preliminaries to the 

 dicentric figures take place simultaneously in the two pronuclei, which, 

 though distant, behave exactly as if they were one. (4) Two nuclear 

 elements, the equivalent of two chromatic loops, are eliminated by the 

 ovum in the formation of polar globules, in such a way that the female 

 pronucleus differs from that of the ordinary cells in including only two 

 instead of four chromatic loops. (5) The male nucleus also includes 

 only two chromatic elements, instead of the four found in the spermato- 

 meres ; like the female pronucleus, it is a seminucleus. (6) From the 

 moment when the pronuclei become spherical reticulate nuclear bodies, 

 kinesis begins. The first embryonic cell capable of division, and poten- 

 tially representing the future individual, is formed at the moment when, 

 at the expense of the remnant of the egg-chromatin on the one hand, and 

 of the spermatozoid-chromatin on the other, two nuclear reticulated 

 elements are formed. Together these represent a complete nucleus. It 

 is quite indifferent whether they approach and fuse ; in Ascaris, in fact, 

 this does not take place in the immense majority of instances. Then 

 there follows a vigorous criticism of Carnoy and Zacharias. His answer 

 to the former does not lack in asperity. 



IV. Metapliasis and Anaphasis. — (1) The doubling of the primary 

 chromatic loops frequently exhibits this peculiarity, that in the blasto- 

 meres the secondary loops may remain united by their extremities, though 

 otherwise distant. As the result of this terminal union a barrel-shaped 

 figure is produced. This may be called the heterotypical form, and is 

 minutely described, (2) In this form the incurved extremities of the 

 secondary loops are never directed directly towards the poles of the 

 dicentric figure, as Flemming represents in the spermatogenesis of Sala- 

 mandra. The constitutive fibrils of the achromatic spindle are clearly 

 contractile. In a large number of cases the primary and secondary 

 chromatic loops are found to be connected by interposed achromatic fibrils, 

 which are probably contractile, and explain the relative displacement of 

 the primary loops preliminary to the formation of the equatorial star. 

 (3) As to the reconstitution of the nuclei derived from the dyasters, what 



