Katharine Foot and E. C. Strobell 231 



In both Oligorlia'tes the chromosomes have a distinct longitudinal furrow, 

 which has persisted in AUolohophora from the skein stage, and in both 

 forms the first division separates two univalent chromosomes. In these 

 two Annelids the achromatic nucleoplasm contributes to the formation 

 of the spindle fibers, the fibers forming within the germinal vesicle 

 while its membrane is partly intact^ and the centriole in both cases is first 

 seen outside the germinal vesicle close to its membrane, though in Ophryo- 

 troclia the two arise by division of one, while in AUolohophora they are 

 first seen at opposite poles of the vesicle. 



Thalassema. — Griffin's interesting paper on the maturation and fer- 

 tilization of the egg of Thalassema, '99, gives a clear demonstration of 

 the prophases of the first maturation spindle. These are reproduced in 

 his Figs. 1 to 12, but Griffin demonstrates no spireme in the germinal 

 vesicle, and he neither figures nor describes stages answering to the 

 stages shown in our Photos. Ill to 115, Plate VII, and in Korschelt's, '95, 

 Figs. 67 to 74. He figures a spireme only in the nuclei of " minute ova,'' 

 the size of these nuclei in relation to the germinal vesicles of later stages 

 showing them to be the young nuclei emerging from the telophase of the 

 last oogonial division, and the spireme of these nuclei is not comparable 

 to the spireme demonstrated in our photographs of Plate VII. They can 

 be compared only to similar minute cells in the ovary of AUoloho- 

 phora. stages with which we are not concerned in the present paper. In 

 the text Griffin describes the spireme of the nuclei of these minute cells 

 as showing an occasional longitudinal split and dividing transversely 

 into bivalent chromosomes at the heginning of the growth, period (Fig. 

 2), these chromosomes persisting ''as double rods throughout the entire 

 growth period" (p. 605). In AUolohophora the chromosomes do not 

 persist through the growth period nor can any indication of the aggre- 

 gation of the diffused chromatin into the spireme of Photos. Ill to 115 be 

 demonstrated until some time after the germinal vesicle has attained its 

 maximum size (see p. 217 for details). The two Annelids agree, how- 

 ever, as to the form of the final tetrads. Griffin's Text Figs. 1 and 2 

 show chromosomes in the form of rings, figures 8, crosses, etc., which 

 are strikingly like those in many of our photographs, though their origin 

 is apparently very different. In Thalassema the spireme divides trans- 

 versely into half the number of somatic segments, these bivalent chromo- 

 somes differing, however, from AUolohophora in the important point 

 that their bivalent character is expressed by a longitudinal division of 

 each, instead of two univalent chromosomes being attached end to end. 

 as in AUolohophora. Thus the rings, figures 8, etc., which are com- 

 mon for the two Annelids have a different origin, necessitating a different 



