Herrick, Morphology of Brain of Bony Fishes. 33 



then imagine an expansion due to a proliferation of the ependyma 

 and great increase of the mass of blood-vessels, while the ectal 

 attachment of the (now greatly elongated) fibres is retained, the 

 suggested origin of the structure will be understood. 



The connection of the fibres with fusiform cells of the mem- 

 brane, at any rate, is perfectly clear, and the obvious interpre- 

 tation of the structure is that it is an outward development of 

 plexus similar to those which fill the ventricles and may have a 

 similar function in the elaboration of a nutrient fluid or the 

 like. 



In a series taken in various directions through the brain of 

 very young and later stages of Amiurus we have a clear illustra- 

 tion of the mode of origin of the two related structures. 



It should be remembered that in the adult catfish the saccus 

 reaches an extreme development, being, as stated by C. Judson 

 Herrick, a mere epithelial sac. In the very young the two 

 bodies spring from the iter infundibuli at the same point, a slen- 

 der canal passing some distance into the anterior (hypophysis) 

 portion which receives abundant connective fibres from the 

 tuber. These fibres are apparently related to the epithelium as 

 above described. From this dorsal expansion there is also de- 

 rived a sac which expands caudad into a small chamber whose 

 walls are convoluted. In this stage it is easy to see that the 

 convolutions are due to the pressure of blood vessels. The 

 cephalic portion is closely associated with the cephalo-ventral 

 aspect of the saccus, while the dorso-caudal portion of the latter 

 is appressed upon the mammillary bodies. 



In a somewhat later stage the sac has enormously enlarged 

 and the enlarged portion is devoid of convolutions but retains 

 the essential characteristics. The glandular portion is also greatly 

 enlarged and its strong peduncle of fibres can be traced along 

 the ventro-cephalic aspect of the tuber and dorsad into the region 

 of the ventral peduncular bundles, accompanied by those of the 

 saccate portion. The glandular portion consists of a closely 

 packed mass of follicles with blood vessels within, the saccate 

 part is a single layered epithelium giving off connective fibres 

 ectad and covered by a reticulum of capillaries ectad of these 

 fibres. It is interesting to observe that the axial part of the 

 glandular part, i. e. that portion derived from the brain and 



