MUSEUM OF COMPARATIVE ZOOLOGY. 431 



occupies the middle of the spindle. Around each of its ends is a clear 

 homogeneous area, and outside this the yolk granules are arranged in 

 radial lines, thus forming two suns. The "area" passes gradually into 

 the surrounding granular yolk. The spindle is the metamorphosed ger- 

 minative vesicle. It is ejected * from the yolk, not in the simple lorm 

 previously described for Cucullanus, but in several vesicular portions 

 which apparently enlarge by swelling up, and are united to each other 

 by narrow necks. The constrictions are due to an active process of 

 nuclear division. Of the three portions of this ejected nucleus (now 

 a polar globule) the first is the smallest, the last the largest. During 

 the early stages of this elimination the part within the yolk retains its 

 spindle form, and a zone of dark granules is found at [near] this end of 

 the spindle, as well as in the part of the polar globule already eliminated. 

 The latter zone is joined by delicate filaments with the filaments within 

 the yolk. Ultimately the whole of the spindle is eliminated. The first 

 and second portions of the polar globules subsequently unite, and a clear 

 vesicle [nucleus] often makes its appearance therein. 



The female pronucleus was observed at an early stage, but no connec- 

 tion with the spindle was detected. The changes in Cucullanus have 

 already (p. 404) been given. I will add, that Biitschli (loc. cit., p. 224) 

 judges, from the appearance of the optical cross-section of the spindle, 

 that the nuclear plate lies within a definitely circumscribed body, there- 

 fore cannot be a simple differentiation in the yolk. The protoplasm 

 immediately underlying the ejected spindle is for a certain distance 

 clearer and more coarsely granular than the rest of the yolk, from 

 which it is quite sharply defined. This clear protoplasm probably 

 spreads over the surface of the vitellus and is the seat of the formation 

 of the new nuclei, since the latter arise close under the surface at widely 

 separated places. 



* I am not quite satisfied what share Biitschli intends to ascribe to the astral 

 rays in this process of elimination. He says (p. 216) : "Etwas spatere Stadien zei- 

 gen nun, dass die um das ein6 Ende des spindelformigen Korpers befindliche Dot- 

 terstrahlung bis in die Oberflache des Dotters geriickt ist und der spindelformig 

 metamorphosirte Kern sich durch diese Strahlung aus der Oberflache des Dotters 

 hervorzuschieben beginnt." I think he has nowhere else intimated that the rays 

 were an agent in the propulsion of a nuclear mass, and it is therefore barely possible 

 that here he only means to say that the nucleus makes its way through (hindurch) 

 the peripheral aster. But the more literal reading makes the rays the agent of the 

 ejection. It is in this sense that 0. Hertwig ('77, p. 5) understands the author when 

 he paraphrases his description by saying : "Die Kernspindel .... wird von einer hier 

 befindlichen Dotterstrahlung aus der Oberflache des Dotters hervorgeschoben." 



