KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 229 
illustration of this process see fig. 14. This does not, indeed, 
refer to Rana but to Ascaris megalocephala, but may serve 
for the above description. 
It is evident that the whole process may in fact be 
regarded as a karyokinetic division of the whole egg-cell with 
very unequal products (Hertwig, Fol, Schneider, Nussbaum)— 
at least so far as regards the cell-substance (see Flemming, ‘ Biol. 
Centralblatt,’ iii Bd., p. 641)—and Oskar Schultze’s researches 
have shown that in every essential the process in Vertebrata 
agrees with what we know for the Invertebrata, from the works 
of Butschli, Fol, O. Hertwig, E. van Beneden, and others. 
We have, besides this, no detailed account of the formation 
of directive corpuscles in Vertebrates, although they have been 
seen by many observers in all classes except Birds and Reptiles 
(cf. the various examples previously mentioned, and Schultze’s 
summary ).! 
“ Richtungsspindeln ” have been observed only by Flemming 
(63 a) and Bellonci (16 a) in mammalian eggs, by C. K. Hoff- 
mann in Teleostei, and by Bohm (1. c.) in Petromyzon. 
As to the formation of directive corpuscles in Ascaris 
megalocephala, E. van Beneden (238) establishes new and 
important facts. Among these are the proof of the origin of 
the spindle threads from a part of the nuclear substance and 
nuclear membrane ; the segregation of the chromatic figure into 
two groups of four chromatin spheres ; the origin of these eight 
spherules from the germinal spot (“corps germinatif” of van 
Beneden) ; the extrusion of four of these chromatin spherules 
to form the first directive corpuscle; the formation of a second 
directive corpuscle with two groups of chromatin spherules, 
which later on divide, so that one half of the spherules of each 
group pass to the second directive corpuscle, and the other half 
‘ In this summary, as well as by Weismann and Ischikawa (204 a), the 
Selachians are omitted ; I therefore mention that Kastschenko, in the number 
of the ‘Anatom. Anzeiger’ (No. 16, July 1st, 1888), issued during the 
correction of these sheets, describes the directive corpuscles in various species 
of Selachians, usually two in number, in one case only one, and in one case as 
many as three, 
