No. 3-] THALASSEMA AND ZIRPHAEA. 6ll 



swelling, and the traction-fibers attached some distance from 

 the distal extremities. Another form (II, x) is similar to one 

 figured by Flemming in the salamander, and considered as a 

 ring split at but one point. Here, however, it evidently has 

 a different interpretation, being probably similar to the above, 

 but under greater tension, and with the free distal ends bent 

 further. Both show the faintest possible indication of a central 

 split. These may be rings just previous to division and after 

 the disappearance of the lateral loops, or those in which lateral 

 loops have failed to develop. In the latter case they would 

 divide transversely, while the remaining chromosomes split 

 longitudinally, and an equation and a reducing division would 

 occur simultaneously in the same spindle — a possibility urged 

 by Wilcox ('95). A third deviation, observed but once, is the 

 thick T'-shaped form (II, y, z), in which the rounded extremities 

 and faint streak in the center of each arm show it to be a ring 

 with but one lateral loop instead of two. Occasionally the ring, 

 failing to develop lateral loops, becomes attached to the traction- 

 fibers, near one extremity (II, z), as Farmer and Moore ('96) 

 figure in the pollen mother-cells of Liliuni, except that it does 

 not break apart at the attached end. The just-mentioned thick 

 Z'-form may represent a more contracted condition of this ring, 

 or may have been derived from one of the open rings. 



After completion of the first division the dyads are taken 

 immediately into the second polar spindle and arranged at right 

 angles to the spindle-axis, with the halves directed toward either 

 pole (PL XXXI, Fig. i8 ; PI. XXXII, Figs. 19, 20). A single 

 traction-fiber is attached to one end of each of the rods. In 

 those on the periphery of the spindle, this is the inner 

 extremity. 1 



The division of the daughter- F"' J in anaphase or telophase 

 recalls Ophryotroclia, except that in Thalassevia the halves 

 remain associated in pairs, and it is certain that one member 

 of each pair, and not a whole pair, passes into the polar body. 



1 In cases where the halves are closely appressed in the middle, and swollen at 

 the extremities, an appearance suggesting tetrads sometimes results. This, I 

 believe, is all the significance there is in " tetrads " described by some authors 

 (eg; Klinckowstrbm, '97) in the second polar spindle. 



