61 
then proves to be right. It seems to me less probable, 
however, that thís mouth would be a secondary one in 
regard to that of Craniates. The latter is found again by 
VAN WYHE in the praeoral or HATSCHEKS pit. He was 
led to thís conclusion on the same a priori ground as is 
adduced by NEAL (see above). According to VAN WYHE 
(1907, p. 69) this change, not of function but, of organ 
would find its cause in the spiral movement of the larva 
during its pelagic life. However plausible this may be 
rendered by VAN WYHE, from the point of view of my 
theory it seems unnecessary to look for any-other forerun- 
ner of the present mouth than ..... the neuropore. After 
the loss of the neuropore, which in young stages still per- 
haps acts as a mouth, one of the gill- 
slits has taken over its function, as ex- 
pressed by a modification ot VAN 
WYHE's sentence, proposed by me 
(1913) in a former paper: “er hat den 
Mund (den Neuroporus!) verloren und 
frisst infolgedessen mit einer Kiemen- 
spalte”. 
First pair of gill-pouches. — If, how- 
ever, as argued on page 271 of this 
treatise, it may a priori be expected 
more orless that the first pair of gill- 
slits would have broken through at the 
limit of the prostomium and the first en 
segment, then we might expect tofind Fis pr rjngdie 
a pair of gill-pouches in front of the of Amphioxus as fig. 
mouth and the club-shaped gland and 23, seen 
in front of the mandibular segment. __dorsal side and sho- 
As such, 1 believe, must we consider, miser nek gnden 
as HATSCHEK (1892, p- 144) originally bantertar entoderm 
did, both the anterior entodermal di- pockets”), the rostral 
verticula. In fig. 23 and 24, after prolongations of the 
HATSCHEK, we see them originate in After HATSCHEK. 1882, 
a strictly bilateral way as evaginations fig. 52. ; 
obal 
S B 
DAE En 
IE 
baton frordep Pec 
of the entoderm just in front of the mandibular somites, 
exactly where and as we should expect a first pair of 
gill-pouches. One of them, the left, still acquires an opening 
to the exterior, the praeoral pit which, according to HATSCHEK 
(1892, p. 144), is innervated in a similar way as the mouth 
