228 First Maturation Spindle of Allolobophora Foetida 



86, 91, 93, Plate V, 99 to 110, Plate VI), but we do not think this 

 necessarily means that these centers are devoid of archoplasin ; it may 

 indicate rather a definite chemical combination with the achromatic 

 cytoplasm that causes a different morphological reaction to fixation 

 (Foot, '96). An obvious contribution of archoplasm to the spheres is 

 largely dependent on fixation, and in some cases it is aggregated into 

 granular masses or heavy rays around the mark-zone (Foot and Strobell, 

 .'00), and again the mark-zone itself is granular and stains intensely. 



Differentiation of a special chromatic substance in the cytoplasm of 

 young oocytes or spermatocytes is very common, but more rarely is this 

 substance traced to the later stages of development. Among recent 

 papers Voinov, '03, has traced a substance to the first spindle in Cybister, 

 and finally to the Kebenkern. He has designated it as " zone interne " 

 as distinguished from his " zone externe " (Figs. 29 and 30), and a com- 

 parison of his figures with our photographs leads to the impression that 

 the archoplasm of AUolodopliora is synonymous with his " Mitochondria " 

 (Benda's) and "zone interne" combined (see his Figs. 35 and 39). 



Data as to the specific nature of polar-ring substance have been pre- 

 sented by Wilson in his interesting paper on Dentalium, '04. He iden- 

 tifies an upper and lower polar area in the oocyte and of these he says: 

 , "I believe it is probable that at least the lower protoplasmic area and 

 probably also the upper disc are in a general way comparable to, if not 

 identical with, the polar rings observed in the eggs of certain leeches and 

 Oligochcetes." Of the lower polar area he says: "It is evident 

 that material from the interior of the egg must flow into the 

 lobe as it forms,'^ and of the upper polar area he adds : " It is here again 

 evident that an extensive flow of this material must take place from the 

 interior of the Qgg" (pp. 12-15). These facts have a special bearing 

 on our interpretation that the polar ring substance is distributed through- 

 out the egg and later aggregates at the poles. (Foot and Strobell, '98-) 

 Wilson interprets both areas as " specific cytoplasmic material." 



In this connection Wheeler's w^ork on Myzostoma, '97, is of special 

 interest. He interprets certain phenomena at the upper pole of the egg 

 as homologous to the polar rings of Annelids and he identifies in the 

 oocyte (Fig. 1) a denser area of protoplasm which strikingly resembles 

 the yolk nucleus of AUolohophora and this he traces to the yolk-lobe 

 (opposite pole), though he does not interpret the substance as yolk- 

 nucleus, nor the yolk-lobe as homologous to a polar ring of Annelids. 

 Conklin, however, in 1897, identifies at the vegetal pole of the egg of 

 Crepidula a mass of hyaline substance which he homologizes to the 

 yolk-lobe described by Mead in ClKBtopterus and to the polar rings of 



