EECENT WOEK ON THE PEOTOCHOEDA. 241 



the first polar body is removed from the surface of the ovum 

 and so is lost.^ 



In their account of the later development, the authors of the 

 Traite have been seriously led astray by the recent work of 

 R. Legros.^ 1 regret to say that this author has produced a 

 paper of a highly destructive character, from which it would 

 appear, to the uninitiated, that his predecessors are incapable 

 observers. As one of his principal results he seeks to show, by 

 transverse sections through embryos preserved in a sublimate- 

 acetic mixture, that the prseoral pit, which is such a distinc- 

 tive feature of the larva of Am phi ox us, arises as a solid 

 ectodermal proliferation which subsequently hollows out. 



Hatschek^s account of the origin of the prseoral pit from the 

 left head-cavity has recently been confirmed by MacBride (loc. 

 cit.) by transverse sections through embryos preserved in osmic 

 acid. 



Hatschek's nephridium, according to Legros, arises as an 

 outgrowth from the alleged ectodermal prseoral pit, and the 

 whole apparatus is subjected to an obvious and well-fitting 

 comparison with the hypophysis of Ammocoetes, and hence 

 with the hypophysis of Craniates in general ; in fact, he makes 

 it identical with the hypophysis of Ammocoetes, thus leaving 

 no room for change of function nor for evolution. 



The orifice of the prseoral pit of Amphioxus, considered 

 as a coelomic cavity opening to the exterior, has generally 

 been supposed to be related to the proboscis-pore of the En- 

 teropneusta.^ From what has been said above (p. 231) it 

 follows that the prseoral pit, like the mouth, has quitted its 



^ Sobotta describes two membranes round the egg, an inner and an outer, 

 but makes no reference to the follicular membrane described and figured by 

 Langerhasn. 



^ Robert Legros, " Developpement de la cavite buccale de I'Amphioxus 

 lanceolatus. Contribution a I'etude de la morphologie de la fete," 

 'Archives d'Anatomie raicroscopique,' tome i, No. 4, 1897; and tome ii, 

 No. 1, 1898. 



* For full treatment of this difficult subject see my memoir entitled 'En- 

 teropneusta from the South Pacific, with Notes on the West Indian Species,' 

 now in the press ; Part iii, Zool. Results. 



