1022 



than is the case before oi- hehiiid the gland. The ring however is 

 not regular. hiU its left side is developed more strongly than the 

 right. Soon however it disappears on the right side and through 

 this the gland becomes asymmetrical. 



As this asymmetry is also found in higher forms e.g. Ammocoetes, 

 it must be independent of the above discussed asymmetry of the 

 branchial gut. 



Finally I should like to point out that another gnt-ring the ilio- 

 colon ring, in the larva with one gill cleft is of importance for the 

 morphology of the alimentary canal in the Vertebrates. In Amphiox- 

 ns this ring indicates the boundary between mid- and end-gut. 



Physiologists have ali-eady long known that the nervus vagus in 

 the higher animals and man helps to supply not only the fore- or 

 "head"-gut, but also the whole mid-gut or "small intestine". Anato- 

 mists as a rule ascribed to the n. vagus the region of the fore-gut 

 only, because the foremost of the two strands which form the con- 

 tinuation of the vagus plexus around the oesoj)hagus, ends on the 

 foremost wall of the stomach, while the hindmost strand is connected 

 with the plexus Solaris of the sympathetic nerve. 



On account of this connection it was impossible to follow with 

 certainty the ramifications of the vagus further distally than the 

 stomach. Our countryman Donkf.r ^) has however lately succeeded in 

 doing this in apes. He could establish the fact that the ramification 

 of the vagus leaches to the end of the mid-gut and that it does 

 not extend to the "large intestine" (end-gut in a broad sense). In the 

 section of his text-book which ap|)eared this year Mekkel also lets 

 the ramification of the vagus in man reach to the end of the mid-gut. 



It is not surprising that the vagus, the tenth cranial nerve, supplies 

 the fore-gut as it is a well known fact that the fore-gut is originally limited 

 to the head region. The question now arises whether the mid-gut 

 was perhaps originally situated in the head region also. To a certain 

 extent the development of Amphioxus can give us an answer to this. 



The ilio-colou ring, which forms the boundary between mid-and 

 end-gut lies more rostrally the younger the larva is. The larva of 

 Lankesteh and Willey with 14 gill clefts already has 61 myotomes, 

 just as many as the adult animal. The ilio-colon ring lies under the 

 34''', 35^1' and 36^'' myotomes. In their larva with 3 gill clefts. and 

 only 36 myotomes the ring lies under the 15^'' and 16'^' myotomes. 



') P. Donker, Uebei- die Beteiligung des N. vagus an der Innervation des 

 Darmes. Anal. Anzeiger, Bd. 51, No, 8, 1918. 



