278 G. E. DE BEER 



evidence is in favour of the cleft representing the true hypo- 

 physial cavity, and to quote Biedl (1913) ' the anterior and 

 posterior lobes are separated by a cleft more or less broad. 

 This represents the vestige of the embryonic hypophysial 

 cavity. The posterior wall of this cavity is directly opposed 

 to the posterior lobe and forms its anterior limit in the shape 

 of a strip . . . known as the pars intermedia.' 



The identification of the hypophysis with Kolliker's pit (and 

 therefore the neuropore) of Amphioxus (Willey 1894) is open 

 to the objection that in higher forms hypophysis and neuropore 

 are found in one and the same animal without any connexion. 



With regard to the Tunicates the researches of Juhn and van 

 Beneden led to these observers believing that the hypophysis 

 is represented by the subneural gland. But the later observa- 

 tions of Willey, Seeliger, and others show that the neural gland 

 is derived not from external ectoderm but from the nervous 

 system. The gland may have some connexion with the neuro- 

 pore, but later it is in communication with the buccal cavity 

 and a shallow ectodermal invagination (or several) meets the 

 tube growing out of the gland. It is possible that the shallow 

 ectodermal invaginations alone may represent the hypophysis 

 (Stendell 1914fc). Dr. Hogben kindly permits me to make 

 use of the fact that he found that extracts from the subneural 

 gland of ascidians had no properties such as are present in 

 extracts of the posterior lobe of the pituitary of all classes of 

 Gnathostomes. 



Dohrn's (1883) view that the hypophysial cavity of Petro- 

 myzon represents a pair of gill clefts is open to the objection 

 that whereas gill clefts are formed by outgrowth of endoderm, 

 the hypophysis is ectodermal. 



Haller (1896) beheves that the hypophysis of Cyclostomes 

 is secondarily modified, but he describes a lumen in the pars 

 intermedia the existence of which has never been confirmed. 



Woerdeman (1914) agrees that the glandular elements are 

 differentiated from a sohd strand of tissue in the absence of 

 any cavity, and also that the greatest part (' Grosstenteils ') 

 of the hypophysial depression is due to the overgrowth of the 



