OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 555 



In Sycon sponges, according to Jorgensen ('10, p. 204), there 

 is a pseudo-reduction followed by a pre-reduction, but not in the 

 Weismannian sense. The true reduction occurs in the oogonia, 

 a conclusion which he states in the following words : — 



In einigen Fallen aber schien es mir so, als ob die etwas langliche 

 Muttertetrade — die wir iins aus zwei langlichen parallel konjugierten 

 Chromosomen, deren jedes aus zwei Chromomeren zusammengesetzt 

 ist, entstanden denken konnen — mit ihrer Langsachse in die ^ pin- 

 delachse eingestellt wiirde. Nach der Verdoppelung der Tetrade zum 

 viersauligen Prisma erfolgt die Teilung gemass dem Querspalte. 

 Diese Teilung wiirde hintereinandergelegene Chromomere eines Chro- 

 mosome trennen, wiirde also eine Reduktionsteilung im sinne Weis- 

 manns. Bei beiden Oogoniengenerationen kann — ^nach meinen Beo- 

 bachtungen — -diese Reduktionsteilung auftreten. 



Each of the two daughter plates of the second maturation 

 division in A. canis (figs. 50 a and 50 b) contains eighteen dyad- 

 like chromosomes, each chromosome being constricted trans- 

 versely by the Querkerbe (figs. 50 and 51). The daughter 

 plates move apart (fig. 51) and the peripheral one with its en- 

 veloping cytoplasm comes to lie in the space between the egg 

 and its fertilization membrane (fig. 52). The interzonal fibers 

 then break down and the detached body secretes a membrane, 

 thus completing the formation of the second polar cell. Mean- 

 while the group of chromosome retained within the egg cyto- 

 plasm is converted into the female pronucleus (fig. 53). I all 

 the material examined the chromosomes of both the polar cell 

 and the female pronucleus are apparently in the clumped con- 

 dition during the late telophase. This apparent clumping of the 

 chromosomes of the female pronucleus is not an actual one, 

 but is due to the very close crowding of the chromosomes, which 

 it becomes very difficult to resolve after staining. 



In all cases the second polar cell remains on the surface of the 

 cytoplasmic mass, while the first one is attached to the inner 

 surface of the fertilization membrane. 



The further development of the female pronucleus will be 

 traced in connection with that of the male pronucleus in the 

 following section. 



