72 P RATHER. [VOL. I. 



The saccus vasculosus begins to form about the tenth clay 

 and steadily enlarges, until at the thirty-fifth day it forms a 

 process of the infundibulum in the shape of a glove-finger, 

 extending directly backwards under the base of the medulla 

 and parallel with the base of the cranium. 



This is very nearly its position in the adult brain as figured 

 by Allis. 1 At no stage, therefore, is it in close association 

 with the hypophysis, which connection is found to be true in 

 so many cases. Abundant granular secretions are found in it 

 at the twenty-second-day stage, and these increase in amount 

 thereafter. 



GENERAL REMARKS. 



The course of development of the hypophysis in Amia as 

 described in the preceding pages, when compared with the 

 descriptions given by other observers, both in Amia and other 

 Ganoids, will be seen to present some striking peculiarities. 



Dean 2 says : " The hypophysis is by no means as important 

 an element in the development of the head in Amia as in other 

 Ganoids. Its appearance is late and inconspicuous. It has 

 not been found in stages earlier than that of Fig. O (JiatcJiing 

 time}? and even here its presence is not definite. At the most 

 the position of its lumen can be recognized as the line HY t 

 formed by the arrangement of cells immediately below the 

 region of the recessus opticus. These cells are apparently 

 ectodermal, for they are arranged in a continuous line with the 

 cells of the formative epiblast of the dorsal wall of the stomo- 

 daeum, but, on the other hand, their ventral limit cannot be 

 distinguished from the entodermal cells roofing the foregut." 



In what respect the development of the hypophysis is less 

 important in Amia than in other Ganoids is not clear. In 

 point of size and position its relations are almost exactly the 

 same as in the other Ganoids, so far as the larval stages have 

 been examined. As for its appearance being " late and incon- 



1 Allis, Edward Phelps, "The Cranial Muscles and Cranial and First Spinal 

 Nerves in Amia Calva," Jonrn. of Morph. Vol. xii, No. 3, PL XXXVIII. 

 1897. 3 Italics are mine. 



2 "On the Larval Development of Amia Calva," Zool. Jahrb., p. 667. 1896. 



