o81 



lias not ('Oiili-adickHl tins coiiciiisioii, l)ii( Mac-Ukidk asserted iiri909 

 tliat in tlie Ampliic^xiis-larva llie niandihular cavity slioiild lie l)eliiiid 

 the nionlli. Wlicn I iiad the |>ri\'ilege of receiNiug a few years ago 

 Amphioxiis-hirxas tVoni tlie Zoological stations at Naples and in 

 Helgoland, niy attention was specially directed to this point, and 

 I fonnd in all the series of my sections of the larval growth-period, 

 but also in tiic beginning of the jiietan]or|)hosis, that the niandibnlar 

 cavity does not rnn bohiiul (he month-opening, as Mac-Bhide asserts, 

 bnt before it. In my opinion it has hereby been definitely proved 

 that the month-opening of the Amphioxns-lai-va is homologons with 

 the left spiracle of Selachians. 



In the conrse of the nietamoi'j)hosis the mandibnlar cavity develops 

 ronnd the mouth, first in the shape of a horse-shoe and after- 

 wards in the shape of a ring, because the extremities of the horse-shoe 

 unite themselves with each other behind the mouth and form the 

 ring-shaped cavity of the velum. As soon as this cavity has assumed 

 the shape of a ring, one can of course no longer see, whether it 

 was situated originally before or behind the luouth. 



Finally I may be allowed to give a short communication of the 

 remarkable variations which the mouth of the larva undergoes, of 

 which we know already from Hatschek that it invaginates to the 

 inside und Irp.nsits into the ring-shaped velum-fold, which, in the 

 full-grown animal, separates the mouth-cavity from the throat 

 (pharynx). This invagination is accompanied, duriug the metamor- 

 phosis, by the formation of a longitudinal fold of the skin, extending 

 along the left side of the mouth of the larva and of the praeoral })it. 



Hereby is formed an open cavity before the mouth of the larva: 

 the month-cavity of the fidl-growu animal, in which likewise the 

 praeoral pit is lodged, and which, by a longitudiiuil slit along which 

 the cirri sprout fortli, opens to the outside. This slit is known 

 as the month-slit of the developed animal. 



At the end of the embryonal period, when the lar\'a is onh 

 1 m.m. long, and the first gill-slit is on the point of opening to 

 the exterior, the mouth is a little almost round opening on the 

 left-side of the body uiuler the second myotome. It lies then oppo- 

 site the club-shaped gland, which is found under the second myotome 

 of the i-ight-side. 



With the growth of the larva the month-opening, which is now oval 

 and becomes afterwai'ds slit-shaped, increases gigauticly in length. 

 When three gill-slits are extant, the mouth reaches as far to the 

 back as the back-i-im of the fii-st slit, and at the end of the larval 

 growth-period it roaches even the back-rim of the fourth or fifth 



