74 P RATHER. [VOL. I. 



the evidence in other types of its being derived from the epi- 

 blast, we should be inclined to regard it as hypoblastic in origin." 

 They speak of it as an invagination of the oral epithelium, with- 

 out stating whether this invagination is anterior or posterior 

 to the oral plate. Presumably from the previous statement 

 they consider it derived from the roof of the foregut posterior to 

 the oral plate. They figure a transverse section of the anterior 

 part of the head of an embryo on the ninth day after impreg- 

 nation, showing an invagination from the mouth roof with a 

 thickened, solid, conical process extending upwards into the 

 cranial cavity. This, with the exception of the invagination, 

 is very similar to its condition in cross-sections of Amia late in 

 the seventh day, passing through the anterior end of the organ, 

 as shown in Fig. 6. They also figure transverse sections 

 through the anterior and posterior ends of the hypophysis of 

 an embryo eleven days old, where in front it is still in connec- 

 tion with the oral epithelium, while behind it is constricted 

 from that layer. These sections indicate relations almost 

 exactly the same as transections of the organ in Amia shown 

 in sagittal section (Fig. 7) at an age of not quite nine days. 

 Comparing these few sections of Lepidosteus and the few 

 words of description with the conditions which I find in Amia, 

 it seems that the hypophysis undergoes a nearly parallel series 

 of changes in the two forms from the time of its primary origin 

 to a late larval stage, but that corresponding embryonic stages 

 are met with in Amia from one and a half to three days earlier 

 than in Lepidosteus, and the corresponding larval stages are 

 found earlier and earlier as the animal advances in age. This 

 justifies, so far as the hypophysis is concerned, Dean's state- 

 ment that " the organogeny of Amia progresses more rapidly 

 than in Lepidosteus." 



I find no lumen earlier than the ninth day, when it appears 

 as a single nearly spherical cavity near the center of the organ, 

 rather than a longitudinal slit, as indicated by Dean in Fig. O. 

 Furthermore, as my sections show, the lumen is never a longi- 

 tudinal slit, even at the late stage of thirty-five days, corre- 

 sponding to Dean's Fig. O of a four-weeks-old larva which 

 shows it as such. Instead of a single lumen at this late period, 



