.^80 



to dasli forward IVoin it \\illi the quickness of an arrow, wlien lie 

 is (listnrl)e(l, and then t(» i-etiirn iuiniediately again into the sand, 

 the reason for asymmetry did not exist any hunger, the gill-basket 

 became symmetrical again, and the month also tried to assnnie 

 a symmetrical position, thongh it conkl only apparently sncceed in 

 it, as it is an organ of the left-side. 



It is not to be wondered at, that there are investigators who 

 o|)pose these views, l)ecanse they cannot admit that snch an ancestral 

 organ, as the primitive month, shonld have had to give way to a 

 secondary month. They admit, that ancestors of Amphioxns, which 

 gave n]) the swimming way of living, have first passed throngh a 

 jjeriod in which they lay on the sand in the way of flat-fishes in- 

 stead of bnrying 'themselves into it; that then the month has removed 

 to the left side, jnst as, with llat-fishes, one eye, which othei'wise 

 wonld be directed downward to the bottom of the sea. removes to 

 the ni>]iei'sid3. 



This theory is untenable especially for three i-easons : 



l^y. The month of the Amphioxus-larva does not originate 

 medianly to remove afterwards to the left-side. It originates on the 

 contrary on the left-side to take afterwards a pseudo-median position. 



2'>' . There is no reason why a median oi-gan. when removing to 

 the left-side should lose its nerves and muscles of the right-side. 

 Not a vestige of such a phenomenon can e.g. be discoxered in the 

 heart and the stomach of man, which are foi- the greater part 

 situated on the left-side. 



3'.^'. One of the ciiaracteristic properties of the second myotome 

 of Seku'hians is the fact, that its cavity remains, for a long time, 

 in communication with the part of the body-cavity that is situated 

 in the lower jaw and is known by the name of mandibular cavity. 

 This communication continues to exist for a long time after the 

 cavities of the following myotomes ha\e sejoined from the body- 

 cavity. 



'J'he same is the case with the larva of Aniphioxus. and in order 

 to make out, whether the mouth of this larva corresponds, either 

 with that of vertebrates, or with their foremost left gill-slit, one 

 need oidy state, whether the mandibular cavity of the Amphioxus- 

 larva is situated t)efore or behind the opening of the nmutli. 



On the base of investigations of Goldschaiidt made on an affined 

 lai'va, called by him Ainphioxides, (and in the begiuiung supposed 

 to be a developed form) I surmised at the time, that I could solve 

 this dilemma in the sense that really the mouth of Amphioxides 

 lies behind the mandibular cavity. In a later publication Goi.dschmidt 



