114 Journal of Comparative Neurology. 



large, dense cell cluster, and is composed of irregular pyra- 

 midal cells (Plate XVI, Fig. 14). In all my preparations 

 these cells are obscurely stained, and have dense, indistinct 

 nuclei. 



Pedimcular niduhis (Plate XVI, Fig. 3; Plate XV, 

 Fig. y). — Laterad to the tract of the third nerve and about 

 half way betw^een the nidulus of that nerve and the base of 

 the diencephalon, there is a large, conspicuous nidulus. This 

 cell cluster has been named by Stieda the " peduncular 

 nidulus." In the blue bird [Sialia sia/is) this nidulus is 

 about 577 micro-millimetres long and about 388 micro-milli- 

 metres wide. The most important elements of this nidulus 

 are large, gibbous, pyramidal cells (Plate XVI, Fig. 9). In 

 different birds the dimensions of these cells vary. In 

 Swainson's thrush [Hylocichla swainsoni) they are about 

 twenty-five micro-millimetres long and about twelve micro- 

 millimetres wide. In the blue bird [Sialia sia/is) these 

 cells are about sixteen micro-millimetres long and ten micro- 

 millimetres wide. When stained with haematoxylin or 

 aluminium-sulphate cochineal, each of these cells pre- 

 sents a densely stained nucleus and more densely colored 

 nucleolus. 



The most conspicuous cells of this cluster are of the above 

 type. But, in addition to these, there are a few cells of a 

 smaller type. In Swainson's thrush [Hylocichla swainsoni) 

 these cells are about fifteen micro-millimetres long and six 

 broad, or only about half as large as the typical cells of this 

 cluster (Plate XVI, Fig. 9), When stained with haema- 

 toxylin or aluminium- sulphate cochineal, these cells present 

 small, densely stained nuclei and denser nucleoli. Although 

 these cells appear to be pyramidal, yet they are so much 

 smaller than the typical cells of this nidulus that one is in- 

 clined to believe that they are physiologically distinct. But 

 the fact that these cells are not universally present in this 

 nidulus, and that diminutive cells are often found in other 

 niduli, gives weight to the idea that these are immature 



