164 Herring 



remains in contact with it. The infundibuknii now begins to grow. In 

 the older embryos, e.g. 11 -mm. sheep, the entodermic part degenerates and 

 appears as a string-Hke appendage of the notochord; it eventually dis- 

 appears, and does not enter into the formation of the adult mammalian 

 pituitary. 



Kupf f er came to the conclusion that the intimate relationship between 

 infundibulum, mouth, and intestine is not an accidental one, but denotes an 

 ancestral communication between the brain tube and the anterior part of 

 the intestinal canal. A structure resembling in many respects the early 

 stao-es of development of the vertebrate pituitary is found in Ascidians, and 

 is known as the subneural gland. Jul in (15) in 1881 pointed out that 

 this gland is probably homologous with the hypophysis of higher vertebrates, 

 and since then it has been frequently spoken of as the Ascidian hypophysis. 

 Kupf f er believes that the direct ancestors of vertebrates showed the same 

 relations as are seen to-day in the tailed Ascidian larva. In a scheme of the 

 ancestral vertebrate he describes the mouth (" Palseostoma ") opening dorsally 

 in front of the brain. The brain tube is in communication with the anterior 

 part of the intestine by a canal running through the base of the anterior 

 brain vesicle. This canal has developed upon it a subcerebral gland. 

 Ventral to the palfeostoma is the " Haf torgan " on the anterior pole of the 

 body. In the course of development the new vertebrate mouth (Neostoma) 

 is formed, in agreement with Dohrn's hypothesis, from a pair of gill- clefts 

 below the " Haf torgan." The part of the intestine between the old and 

 the new mouth, or preoral intestine, is reduced, but persists to a certain 

 extent in some vertebrates. The palseostoma is lined by epidermis, and its 

 representative in vertebrates is Rathke's pouch ; it also forms the outer part 

 of the nasal duct (" Nasenrachengang") of Myxine, and the entire nasal 

 duct of Petromyzon. The remains of the canalis neurentericus anterior, 

 with its appertaining glands, are to be seen in the infundibular process and 

 saccus vasculosus. In mammals, the only representative of the preoral 

 intestine is the transitory appearance of the solid mass of cells formed from 

 Seessel's pouch, but in amphibians it persists as part of the anterior lobe of 

 the pituitary. 



Kupf f er's views on the morphological significance of the pituitary body 

 have not met with general acceptance. Willey (36) states that the present 

 relation of the hypophysis to the infundibulum in the craniates, however 

 intimate it may be in some cases, is, nevertheless, incidental and secondary. 

 Willey believes that the hypophysis arose in connection with a functional 

 neuropore. B. Haller (13) criticises Kupff er's results and differs from him 

 in many important particulars. He believes the nasal duct of Cyclostomata 

 to be a secondary structure and not related to the origin of the hypophysis. 

 He also states that the anterior lobe of the pituitary of mammals and 

 other vertebrates is a tubular gland which pours a secretion into the 

 subdural space. The latter statement has not been confirmed by subse- 

 quent observers. Gaskell (9) quotes Hall er's results in support of the 



