Katharine Foot and E. C. "Strobell 225 



Plethodon. McClimg, 'oo-'o2, lias shown rings, figures 8 and crosses 

 in certain insects clcarl}' demonstrated by excellent photographs. Helen 

 Dean King, 'oi, has demonstrated the ring in the egg of Bufo, and her 

 interpretation that the knob-like thickenings represent " the place of 

 union of the two chromosomes that fused to form the ring " is confirmed 

 by the photographs of our Plates VII and VIII; in Allolohophora, how- 

 ever, the rings do not divide longitudinally in the first division as in 

 Bufo. 



Many forms of the chromosomes in Allolohopliora are similar to those 

 demonstrated by Korschelt, '95, in Opliryotrocha and his interpretation of 

 the first division separating two univalent chromosomes is confirmed by 

 the photographs of our Plates VII, VIII and IX. Further details in 

 wdiich Korschelt's observations are supported by this egg are stated under 

 the heading " Comparisons with other Annelids." 



ArcJio plasm.- — In earlier papers we have used Boveri's, '88, term 

 archoplasm for that substance in the cytoplasm which in the youngest 

 oocytes is massed in different shapes close to the germinal vesicle (yolk 

 nucleus of authors). As the egg grows this substance increases in 

 amount, becomes distributed throughout the cj^toplasm; after fertiliza- 

 tion much of it gradually segregating to the periphery, and finally a large 

 part of it contributing to the formation of the polar rings. We use the 

 term archoplasm because at definite phases of the development of the 

 egg the substance appears to contribute to the formation of asters and 

 spindles and may thus be the homologue of Boveri's archoplasm. • Pro- 

 gressive steps in the development of the substance from yolk nucleus to 

 polar rings were illustrated b}' a series of photographs (Foot and 

 Strobell, '01), but in the present paper we have reproduced only three 

 sections of the earlier stages, merely to illustrate our interpretation. At 

 the upper periphery of Photo. 12 about half of a very small oocyte is 

 shown, with a mass of archoplasm (yolk nucleus) at the opposite poles of 

 its nucleus. . The next stage represented in this paper is shown in 

 Photo. 7G, Plate IV, the archoplasm being somewhat removed from the 

 nuclear membrane. A later stage is seen in Photo. 78, Plate IV, in 

 which the substance is distributed throughout the cytoplasm, and Photo. 

 12 shows a like distribution in an older oocyte. In recent investigations 

 of this polar-ring substance w^e have attempted no analysis by compli- 

 cated methods of staining, studying it only in the light of comparative 

 fixation and aiming thus to demonstrate its presence in eggs in which, 

 after some fixatives, its identity is questionable. 



It is interesting to compare the effects of fixation on the two con- 

 stituents of the cytoplasm, chromatic arclioplasm and relatively achro- 



