6o8 



GRIFFIN. 



[Vol. XV. 



with greater or less clearness to be divided into halves by a 

 pale longitudinal streak extending along the middle. Viewed 

 laterally, these arms are quite thin, and invariably single (PI. 

 XXXI, Fig. II, r). The broad lateral arms, also of varying 

 length, appear in general quite solid, although occasionally 

 what seemed like a similar streak was observed to divide them 

 in halves (/>). Rarely straight, and in the same plane as the 

 polar arms, they are more often curved or bent toward each 



Fig. II. — The chromosome groups (tetrads) of the first maturation-division in Tkalaisema. 

 The narrow lines represent the traction-fibers ; o, early, /, late typical cross ; q, curved 

 cross ; r, curved cross with fused lateral arms in lateral view ; j, the same seen from 

 above ; t^u, origin of the cross from rod-form ; v, early stage of curved cross ; w-z, un- 

 usual and asymmetrical forms. 



other {q, v). By increased bending, the arms may come into 

 contact, whereby a chromosome, J'-shaped, in lateral view 

 results (r, s). Similar J'-shaped chromosomes, but without the 

 distal knobs, are figured by Fick ('93) in the corresponding divi- 

 sion in the Axolotl. Moore ('95) also obtains not dissimilar 

 figures in the Elasmobranchs, and interprets them in an analo- 

 gous manner.^ 



1 The possibility is not completely excluded that these T'-figures may be due to 

 a second longitudinal division of the ring, the two double halves immediately 

 diverging. In view, however, of the prevalency of the crosses and other shapes, 

 in which a second longitudinal division is excluded, it seems more probable that 

 the above interpretation is the correct one, unless, indeed, we accept the possi- 



