Entwicklungsgeschichte d. llerzeua u. der Blutgefäße bei den Selachiern. 615 



ihr späteres Schicksal habe ich nicht untersucht, nur so viel kann 

 ich angeben, dass die Wände dieser accessorischen Kopf höhle bei 

 Embryonen aus Stadium XII fast den der anderen gleich geworden 

 sind und dass sie im Verhältnis zu der ersten Kopf höhle jetzt be- 

 deutend au Umfang bei dieser zurücksteht. Ich kann also die Ent- 

 deckung von Miss J. Platt (Anat. Auz. 1891 ; Journal of Morphology. 

 Vol. V. 1891) vollkommen bestätigen, dass bei Acanthias vor der 

 ersten Kopfhöhle van Wijhe's noch eine gelegen ist, Miss Platf 

 hat dieselbe als »Anterior headcavity« bezeichnet. Killian Verh. 

 anat. Ges. München 1891) hatte ihre Existenz schon vermuthet. 



Über die Entwicklungsgeschichte des Herzens sagt Balfour (1) 

 Folgendes: The first trace of the heart becomes apparent during 

 stage G, as a cavity between the splanchnic mesoblast and the wall 

 of the gut immediately behind the region of the visceral clefts. The 

 body- cavity in the region of the heart is at first double, owing to 

 the two divisions of it not having coalesced ; but even in the earliest 

 condition of the heart the layers of splanchnic mesoblast of the two 

 sides have united so as to form a complete wall below. The cavity 

 of the heart is circumscribed by a more or less complete epithelioid 

 (endothelial) layer of flattened cells, connected with the splanchnic 

 wall of the heart by protoplasmic processes. The origin of this 

 lining layer I could not certainly determine, but its connection with 

 the splanchnic mesoblast suggests that it is probably a derivative of 

 this. In front the cavity of the heart is bounded by the approxi- 

 mation of the splanchnic mesoblast to the wall of the throat, and 

 behind to the stalk connecting the alimentary canal with the yolk- 

 sack. From the above account it is clear that I have failed to find 

 in Elasmobrauchs any traces of the two distinct cavities coalescing 

 to form the heart, such as have been recently described in Mammals 

 and Birds; and this, as well as the other features of the formation 

 of the heart in Elasmobranchs. are in very close accordance with 

 the careful description given by Goette of the formation in the heart 

 of Bombinator. 



In seiner vergleichenden Embryologie (2) giebt er folgende, etwas 

 abweichende Beschreibung: The inner epithelioid tube takes its 

 origen at the time wenn the general cavity of the heart is being 

 formed by the separation of splanchnic mesoblast from the hypoblast. 

 During this process a layer of mesoblast remains close to the hypo- 



