12 G. CARL HUBER 



division Sobotta and Burckhard regard as a reduction division, 

 a heterotypic longitudinal division ; the second as an equatorial 

 division, a homeotypic longitudinal division. Ovulation prob- 

 ably occurs during the monaster stage of the second maturation 

 division. 



The tubal ova are surrounded by a relatively thin oolemma 

 to which are adherent a variable number of discus cells. They 

 are smaller than the ovarian ova; the latter measuring 60 M to 

 65 /*, the tubal ova 55 M to 6(V The recently discharged tubal 

 ova are to be found in the distended ampullar portion of the 

 oviduct, where they are found clumped together surrounded 

 by discus cells. Semination takes place in this region. The 

 spermatozoa usually enter while the tubal ova are in the mon- 

 aster stage of the second maturation division, after which meta- 

 kinesis begins. The second maturation spindle assumes a radial 

 position in the metakinctic phase. The second polar body is 

 smaller than the first, and usually lies compressed between the 

 oolemma and the ooplasm, and is evident during fertilization and 

 segmentation. The spermatozoan head penetrates the thin 

 oolemma and the ooplasma; the long middle piece and tail 

 following the head into the ooplasma, as has been shown by Coe, 

 and Kirkham and Burr. The long middle piece, soon after 

 penetrating the ooplasma, presents an increase in stainability, 

 and its spiral thread becomes evident. The spiral thread, as 

 Duesberg has shown, has its origin in the mitachondria of the 

 spermatid. It may be, therefore, that the male sexual cell 

 introduces mitachondria to the egg cell at the time of fertilization. 

 Some little time after the penetration of the sperm head, this 

 enlarges and becomes vacuolated, and diplosomes with polar 

 rays become evident. As the sperm head begins to metamor- 

 phose, tending to the formation of the male pronucleus, the chro- 

 mosome group of the dispireme of the second maturation spindle, 

 undergoes metamorphosis to form the female pronucleus. This 

 enlarges rapidly to form a vesicular nucleus which lies free in the 

 ooplasm, while the metamorphosing male pronucleus, usually 

 smaller, is accompanied by a deeply staining thread-like struc- 

 ture, derived from the middle piece. The centrosomes of the 



