184 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Riickert. Change of view is no dishonor but a sign of courage, and I 

 respect any man for it, for it is not easy to discard an idea for which 

 one has fought; but in scientific thought we expect change of view to 

 be an accompaniment only of the discovery of more urgent facts. 

 Such facts we do not find in Hacker's latest work (1902, 1904). He had 

 previously observed that in Cyclops brevicornis the normal number of 

 chromosomes is twelve, and that in the ovocytes before the maturation 

 divisions there are six bivalent ones; that these divide equationally 

 in the first and reductionally in the second spindle, so that the ovotid 

 receives six univalent ones. But now he maintains this is wrong, that 

 the chromosomes at all periods of the first ovocyte while bivalent are in 

 the normal number, and that there is no union of them into pairs during 

 the growth period. I have already criticised (19046) this view, and 

 in his retort (19046) Hacker has failed to take up the cardinal issue and 

 give further proof. He describes (1902) that in the ovocyte these 

 twelve bivalent chromosomes are arranged in two planes of six each. 

 This is not borne out by his figs, 30-34. He came to this strange con- 

 clusion in a roundabout way from observations upon the gonomerity 

 of the nucleus, holding that even at the time of the first maturation 

 division the chromosomes are arranged in two planes, corresponding to 

 the earlier gonomeres of the nucleus, one layer of them being maternal 

 and the other paternal. The only evidence for this are certain lines 

 or septa said to divide the ''provisory division figure" transversely and 

 longitudinally. No one has corroborated the existence of such septa, 

 and I have looked in vain for them upon a number of objects ; he gives 

 only lateral views of these structures, does not show their origin, and 

 does not make it plain whence their substance is derived. Yet, fairly 

 speaking, this may be said to be the whole observational basis for his 

 new involved analysis ! Each ovocyte of the second order is said to 

 receive twelve bivalent chromosomes; and then follows a union of 

 tetrads into pairs. ''Bei der ersten Richtungsteilung gelangen, wie 

 bei jeder anderen Kernteilung, je 6 vaterliche und 6 miitterliche Ele- 

 mente in die Tochterkerne, jedoch erfolgt die dicentrische Wanderung 

 nicht in zwei gesonderten, den elterlichen Anteilen entsprechenden 

 Gruppen, sondern die vaterlichen und miitterlichen Elemente miissen, 

 ihrer Aufstellung in den zwei Frontenentsprechend, zwischen einander 

 durchtreten und sind also vollkommen durcheinander gemischt, 

 wahrend sie an die Pole wandern (Textfig. Cb). Diese Mischung ist 

 jedoch, wie wir gesehen haben, keine unregelmassige. Denn es liesst 

 sich mit gr5sster Wahrscheinlichkeit zeigen, dass bei der unmittelbar 

 folgenden Paarung der Spalthalften die Paarlinge jewcils zwei im 



