238 c. o. WHITMAN. 



analogous. By the time the rings have reached tlie stage of 

 fig. 28, the zone of protoplasm (/> z) underlying the oral ring 

 begins to plunge into the yolk, and a little later often presents 

 the forms seen in figs. 70 and 71, which remiiid one of the 

 " sichelformige Auss'rahlungen" seen by Schultz (44t) under the 

 germinal disc (Torpedo). 



The nucleus presents essentially the same appearance in all 

 the istages from fig. 67 to fig. 70; but in fig. 71 P., it has 

 already stretched considerably in a direction perpendicular to the 

 axis of the ec^<j:. The nucleolar bodies are of about the same 

 size and maintain about the same position m all these stages, 

 (figs. 67—71). 



1 will now state my reasons for regarding these three small 

 bodies as nucleoli rather than nuclei. Biitschli and Ilertwig 

 have seen in the egg of Nej^helis two radial systems (" Strahlen- 

 systeme "), and in each system one or more minute corpuscles, 

 which grow at the expense of these systems. The "strahlen- 

 systeme" with their central corpuscles correspond without 

 doubt to the bodies which I have called pronuclei and pronu- 

 cleoli. Hertwig and Biitschli both agree in interpreting these 

 small bodies as nuclei, {-^-\, ii). Hertwig has studied the same 

 phenomena in the egg of Toxopneustes, Asteracanthion and 

 Sphaerechinus, and has here described as " Spcrmakern " 

 (__7_o_-j_7jj-J and '-'Eikern" (jVt» vtV) bodies comparable with 

 the male and female pronucleoli found in the pronuclei of stage 

 66, PI. XIII. Biitschli's interpretation of these corpuscles as 

 nuclei is maintained on the ground, that when treated with 

 ascetic acid (1 ^) they exhibit a thick dark membrane which 

 incloses a fluid with a few dark grai\ules ; and further, that they 

 increase in size at the expens-e of the central area (" Centralhof ") 

 in which they arise. AH these points except the last, have 

 already been disposed of by the observations of Hertwig (4|). 

 Hertwig found that, when treated with osmic acid, these cor- 

 puscles appear thoroughly homogeneous, presenting no thick 

 membrane ("lliille"), as described by Biitschli, but only a 

 somewhat thicker peripheral layer (" Rindenschicht ") ; further, 

 that fJ/e^ do not coalesce uul'il iJieJirsf cleavage- spindle legivs to 

 form.. This is in harmony with what hap])ens in the egg of 

 Clepsine, and corroborates the view I have taken. Hertwig's 

 remarks awaken the suspicion that Biitschli was misled by arti- 

 ficial appearances in regard to the non-persistence of the cen- 

 tral area. 



The enormous size of these cori)uscles in the figures of 

 Biitschli is possibly only a swollen condition produced by Ins 

 re-agents. Such artificial pictures might easily mislead one 

 into the belief that the central area was disappearing. 



