70 Swale Vincent and F. D. Thompson. 



of the pigeon (PI. IV, fig. 7). Though in many regions irregulaily mixed, 

 each is distinct and easily recognised. 



So far as we have been able to observe, the dark columns (bathy- 

 chrome tissue) are peimanent and do not alter with changed physio- 

 logical conditions^), while the leptochrome islets undergo marked vaiiations 

 which are to be described later. 



At the splenic end of the pigeon's pancreas the bathychrome tissue 

 is irregularly distributed throughout the parenchyma of the gland, 

 mostly in the form of a thick irregular interlacing network. Some- 

 times the leptochrome islets are hollowed out in the dark network 

 and groups of dark cells frequently encroach upon the light islets. 

 Further the bathychrome cells are often accumulated, especially at the 

 periphery of the organ, into more solid masses. This condition is seen, 

 however, much more typically in the middle region of the gland, where 

 large solid columns are seen running into the interior of the organ, and 

 giving off in an arborescent fashion the thick network just described. 



In some places a very peculiar picture is presented. In the midst 

 of such a solid column as just described, is seen an island composed 

 f')r tlie most part of ordinary zymogenous tissue, which has, however, 

 a stem or core composed of the bathychrome tissue. This last may 

 sometimes be seen in direct continuity with the zymogenous tubes. 



The bathychrome tissue just referred to appears, when one of the 

 larger areas is examined, to show no cell outlines, but consists of a 

 syncytium of peculiai' mottled protoplasm with numerous rounded nuck^i 

 containing nucleoli (PI. IV, fig. 8, lath, ^yn) The general appearance 

 is admirably described by the word „trouble'', which was applied by 

 Laguesse to the protoplasm of his primary islets. The ground-substance 

 is mottled with whitish granules and vacuoles. 



Ill one specimen at the free end of the pancreas was accumulated 

 a particulaily large mass of the bathychi-ome syncytium, which was visible 

 to thr naked eye on removing the oigan from the body. It formed a very 

 continuous solid-looking body 1 '/o "i"^ ^^ diametei-, but was joined 

 oil ill (;(^jtriiii dii(;ctions to the branching columns already described. 



') Pncentlv we li;ivc susiicctcd tli;i(. on llic cdiil i;irv, tliis tissiii' iii;iy lif in- 

 creased liy inanition. INolc addid Jan. 1. l'.tU7.| 



