76 Swale Vincent and F. D. Thompson, 



On reference to PI. IV, fig. 16, it will be seen that the tissue 

 immediate!}'' surrounding- the circlets of pale cells, constituting in our 

 view the leptochrome islets, is by no means readily recognisable as 

 zymogenous tissue. Its structure is difficult to interpret, but, it seems 

 clear that large tracts of the pancreas in Plethodon are composed 

 of masses of large polyliedr-al cells, bearing very much the relation to 

 the capillary blood-vessels which the cells of the acini bear to their 

 lumen, in other parts of the gland and in other animals. It is inte- 

 resting in this relation to note that in these elongated cells placed 

 round a capillary the nucleus is placed at the end of the cell remote 

 from the blood-vessel. This arrangement frequently obtains with ap- 

 proximately the same depth of staining reaction as in the ca^e of the 

 zymogenous tissue (see PI. V, fig. 15). It is a reasonable hypothesis 

 that this kind of structure may have an endocrine function, perhaps 

 of the same nature as, perhaps different from that of the leptochrome 

 and bathychrome tissues. 



E. Fishes. 



Owing to our distance from the sea-coast we have been unable 

 to obtain any of the cartilaginous fishes for examination. Among 

 Teleostei the following Physostomi have been examined: 



Amiurus vulgaris 

 A. nigricans 

 Moxostoma aureolum 

 Catostomus teres 

 Hyodon alosoldes 

 Efiox lucius. 

 Physoclysti: Stizostedium vitreum 

 S. canadense. 

 As for Ganoidei, in the family Acipenseridae we have examined 

 AcijiPMser rtdncundus, in the family Amiidae, Amia calva. 



lleiinie') and Diamare-) have given careful descriptions of the 

 islets in teleostean fishes, hut since we diOvi' from these observers on 



•) Quart, .loiini. Micr. Sci. Vol. 4S, l';ut. Ill, Nov. IDOl. 

 ') Loc. cit. 



