OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 551 



fertilized. No cases were found in which the first maturation 

 division occurred before insemination, and in all eggs which 

 failed to become fertilized the nucleus broke down without any- 

 further development. 



Kultschitzky ('88 c) and Lukjanow ('89) find that in A. mar- 

 ginata the sperm always enters the egg before the first polar 

 cell is given off and often before the egg nucleus has migrated 

 to the peripher}^ of the cell. The same is true for A. lumbri- 

 coides, and also for A. megalocephala, although here the first 

 polar cell may have been ready to be cut off before the sperm 

 has entered (Van Beneden, '83; Carnoy, '87; Boveri, '88; Hert- 

 wig, '90; Zacharias, '12 d; et ah). Zacharias ('12 d, p. 357) 

 definitely states: — "Bei unbefruchtet gebUebenen Ascariseiren 

 kommt es iiberhaupt zu keiner Ausstossung von Richtungs- 

 korpern " 



The grouping of the spindle fibers for each chromosome now 

 disappears, so that no differentiation between mantle fibers and 

 central ones can be noted (figs. 35 and 37). 



From, the time of insemination until well into the segmenta- 

 tion stages, the alveolar nature of the cytoplasm is very appar- 

 ent, the walls of each alveolus being heavily granulated. Fig- 

 ures 36 and 37 show under higher magnification face and edge- 

 wise views, respectively, of the metaphase plate just as division 

 begins. The face view shows the Querkerbe, no longer a constric- 

 tion in the short axis, as a very faint line, best seen at the periphery 

 of the chromosomes. The deep cross constriction marks the 

 line of the original 'side by side' union of the prophase tetrads. 

 Figure 38 is a side view of the spindle in the late metaphase, 

 showing the chromosomes pulling apart, but still connected by 

 linin bridges. 



The conditions of the formation and division of di-tetrads 

 hitherto described in other animals are as follows: Marcus ('06, 

 fig. 40) has shown that in the metaphase plate of his A. canis (?) 

 the octad chromosomes arrange themselves with their long axes 

 at right angles to the spindle fibers, just as in my own observa- 

 tions on the true A. canis. These fibers are arranged in bundles, 

 one of which is attached to each side of ever}" chromosome. At 



