IQO J^. MITSUKURI; 



Birds' egg is hoinoL^gous with that of Elasin(3])i-anchii. This, as I 

 have said, goes fl:itW against my idea, that the yollv-mass of the 

 Sauropsida is secondary and that Avhich corresponds to the yoUv- 

 mass of Elasmohranchii exists in the rudimentary f(jrm. Future 

 investigations must decide which is con-ect. Tlie distinguished 

 American morphologist himself will, however, he willing-, I think 

 to admit that the results ohtained from the painstaking ohservations of 

 numerous embryos in three different species both in surface-views and 

 sections are entitled at least to as much weight as the observation 

 which, the author himself regrets, is confined to the surface oljservation 

 of a single specimen mounted in toto, entirely unsupported by sections. 

 1 think it just possible that when more is known about the history 

 of the acquisition of the .s<?c'o/?J(//7/ i/olk-iuass in tlie sauropsidan eo-o-^ 

 some f icts reconciling the observations of Wiiit.max with those made 

 by myself may be discovered. This, I think, is all the more possible, 

 because I have never yet observed a distinct posterior boundary in the 

 remnant of the primary yolk-mass in Chelonia, and the long streak 

 on the floor of the posterior amniotic tube in Clemnnjs may, perhaps, l)e 

 explained in connection with that streak observed by Wiiit.max. ]jut 

 for the present this must remain a mere conjecture. The C(3unter 

 Cjuestion : " If the facts brought out in the ])resent article liave not 

 the significance assigned them liere, how then are they to be ex- 

 plained? " would be worth a consideration in decidino- the m:itter. 



THE MAMMALIA. 



in regard to this group, I shall confine myself only to the remark 

 that the mammalian egg is acknowledged by most writers to be 

 derived from a meroblastic egg by the gradual loss of the yolk-mass. 

 If the views set forth above are correct, it nuist therefore be looked on 



