190 THE PITUITARY BODY. 



rectness of the above account, and demonstrate that it is from 

 the mouth invokition, and not, as has usually been stated, from 

 the alimentary canal, that the pituitary body is derived. 



This fact was mentioned in my preliminary account of 

 Elasmobranch development^; and has also been shewn to be 

 the case in Amphibians by Gotte^ and in Birds by Mihal- 

 kowics^ The fact is of considerable importance with reference 

 to speculations as to the meaning of this body. 



Plate XIV. fig. 7 represents a transverse section through the 

 head during a stage between I and K ; but, owing to the cranial 

 flexure, it -cuts the fore part of the head longitudinally and 

 horizontally, and passes through both the fore-brain {fh) and 

 the hind-brain {iv. v.). Close to the base of the fore-brain are 

 seen the mouth (m), and the pituitary involution from this 

 (pt). In contact with the pituitary involution is the blind an- 

 terior termination of the throat, which a little way back opens 

 to the exterior by the first visceral cleft (i. v.c). This figure 

 alone suffices to demonstrate the correctness of the above ac- 

 count of the pituitary body ; but the truth of this is still further 

 confirmed by other figures on the same plate (fig. 9 a and 

 12m); in which the mouth involution is in contact with, but 

 still separated from, the front end of the alimentary tract. By 

 the close of stage K, the septum between the mouth and 

 throat becomes pierced, and the two are placed in communica- 

 tion. This condition is shewn in PL xiv. fig. 16 a, and PI. 

 XV. fig. la, Ic, pt. In these figures the pituitary involution 

 has become very partially constricted off from the mouth in- 

 volution, though still in direct communication with it. In 

 later stages the pituitary involution becomes longer and dilated 

 terminally, while the passage connecting it with the mouth 

 becomes narrower and narrower, and is finally reduced to a 

 solid cord, which in its turn disappears. The remaining vesicle 

 then becomes divided into lobes, and connects itself closely with 

 the infundibulum (PL xv» figs. 5 and 6 pt). The later stages 

 for Elasmobranchs are fully described by W. Miiller in his im- 



1 Quarterly Journal of Microscopic Science, Oct. 1874. 



2 Entivicklungsgeschichte der Unke. Gtitte was the first to draw attention to 

 this fact. His observations were then shewn to hold true for Elasmobranchs 

 by myself, and subsequently for Birds by Mihalkowics. 



3 Arch. f. viicr. Anat. Vol. xi; 



