1020 



which side of the body the extremelj fine anal aperture was situated, 

 because it could on\y be observed in profile, thus by focussing the 

 niicrosope alternatively. 



After however using strong oil-immersion systems (e.g. Zeiss obj. 

 V'i2 oc. 4) the situation of the anus on the right side of the body 

 could clearly be seen also in these preparations. 



When the anus has just made its appearance the tail-fin does not 

 yet reach rostrally to it, but this is soon the case, even when there 

 is only yet one gill cleft present. The anal aperture then lies on the 

 right side of the tail-fin. Here it is also found in larvae with 2, 3, 

 4, 5 or 6 gill clefts. 



Now however the remarkable phenomenon presents itself that it 

 removes to the left side. In larvae with 7 gill clefts a lacuna arises 

 in the tail-fin at the level of the anus, so that the tail-fin is inter- 

 rupted at this place. The anus now enters this lacuna and thereby 

 assumes a mesial position in relation lo the body. This position is 

 however of short duration. With the presence of 9 gill clefts the 

 anus has already passed over to the left side, where it is further 

 permanently found. The lacuna in the tail-fin vanishes and leaves 

 no traces of its former existence. 



I cannot give a reason for this removal. It must stand in con- 

 nection to the manner of life, of which we know little or nothing. 

 This does not however affect the priticipal question, the original 

 situation on the right side, as it was postulated by the theorj'. 



If the theory is not accepted then there is here especially occasion 

 for speaking of a development ''without rhyme or reason". 



In the theory there is in any case a "reason" for the initial 

 situation of the anus even if it cannot "rhyme" its permanent 

 position with this fact. 



The question whether a pancreatic gland occurs in Amphioxus 

 does not stand in relation to the asymnietiy discussed above. 



This gland is known in all the Craniota, from the Cyclostomata 

 to man, but it is the common opinion that it is not present in 

 Amphioxus. 



It arises in the Craniota as one or more bulbs protruded out of 

 the gut epithelium in the immediate neighbourhood of the aperture 

 of the ductus choledochus, which as a rule later on also forms an 

 opening of the pancreas. 



In the Lampreys, which in connection with Amphioxus must be 

 considered in the first instance, the gland is not very voluminous. 

 This must partly be ascribed to the fact that their pancreas, like 



