10 ART. 11. — S. HATTA. 



taking place in the opaque hemisphere ; he gives, though briefly, 

 an account of the depression of the lower hemisphere. Six of 

 his figures {Figs. 4-5«, Taf. II.) show a close resemblance to 

 those of the earlier stages of mine and at least attest his correct 

 observation. 



The accounts given by Goette are, on the other hand, more 

 accurate ; he says : " Diese (the first indication of the archenteron) 

 besteht in einer queren, halbmondförmigen Furche, welche aufwärts 

 gegen den Vorsprung oder die künftigen Rückenseite des Embryo 

 durch eine wulstige Lippe begrenzt, deren seitliche Fortsetzungen 

 aber nach unten gegen die spätere Bauchseite unmerklich verstrei- 

 chen. Dies hängt zusammen, dass die Furche, indem sie sich 

 taschenförmig vertieft, dabei die Richtung konzentrisch zu der 

 oben gezeichneten Rückenfläche des Embryo einschlägt, also 

 ventralwärts flach abläuft. Diese spaltförmige Tasche ist die 

 Urdarmhöhle, ihre äussere Oefl'nung das Prostoma "^\ These lines 

 are, it is obvious, to some extent in accordance with tlie state- 

 ments given above by me concerning early stages. To my great 

 regret, he gives no account of the further changes of the semilunar 

 furrow which " ventralwärts flach abläuft," notwithstanding the 

 fact that these changes represent, in my opinion, one of the most im- 

 portant points of the gastrulation, by which the Petromyzon ovum is 

 put in sharp contrast to other ova of unequal-holoblastic segmenta- 

 tion, for instance, of the Anuran. First of all, the flattened yolk- 

 hemisphere in Petromyzon is converted, towards later stages, into 

 a deep and hollow depression, so that it is, as shown above, never 

 brought into the form of a yolk-plug throughout the whole 

 phase of gastrulation. This fact evidently shows a great activity of 

 the opaque hemisphere itself, by Which activity alone the invagi- 



1) loc. cit., p. 2. 



