128 



THE ANCESTRY OF VERTEBRATES 



and the other gill-slits, viz : by a visceral branch from a spinal 

 nerve (a statement which has not been confirmed by 

 VAN Wyhe, 1893, p. 160). The development of the other, 

 which passes into the praeoral coelome, takes a quite 

 different course. That, however, gill-pouches may give 

 rise to very singular structures is rendered probable by 

 Spengel's (1904) and GOETTE's (1905) derivation of the 

 lungs of Amphibia from a posterior pair of gill-pouches. 

 This idea was rejected by Greil (1906), but MARKUSCHOK 

 (1911, 1912) has confirmed the agreement of the first 

 rudiment of the lungs in Amphibians with a hindmost 

 pair of gill-pouches. 



proot. 



br.l' br.2' br.a"" 



Fig. 25. Left-sided view of a young larva of i4wp^/oxws, showing 

 the first (br. 11, Hatschek's groove), the second (br. 

 21, mouth) and the third (br. 31) gill-opening of the 

 left side and the second (br. 2r, club-shaped gland) 

 of the right side, prost. prostomium. 

 (after Hatschek, 1882, fig. 63 A). 



Thus in fig. 25 (HATSCHEK, 1881, fig. 63 A) three 

 gill slits of the left side have broken through : HatscHEK's 

 pit, the mouth and the first proper gill slit, all three of 

 which may be united by a straight line which, prolonged 

 on the right side, would indicate the situation of the 

 subsequent gill-slits of the left side. The HATSCHEK's pit 

 originally lies right under the neuropore, i:e. exactly at 

 the limit of soma and prostomium where, according to the 

 above considerations, it might be expected. 



If then our conclusions are right, both the anterior entoderm 

 pockets situated in front of the first pair of somites are to be 

 compared with the mouth of Craniates. This is a partial confir- 

 mation of the opinion of VAN WYHE who considered the latter 

 as the left one of the two pockets and, by his desire to find the 

 unpaired Craniate mouth, was induced to doubt the paired 



