On the Relations between the „Islets uf Langerhans" etc. 71 



The i)i'incipal mass is not subdivided bj^ any connective tissue septa 

 and we cannot be sure that there are any capillaries coursing through 

 it, though one or two red blood corpuscles are visible in the section 

 (PI. IV, flg. 8, hid. c). Embedded in it also are several highly refrac- 

 tive spherical cells surrounded by clear spaces and containing a distinct 

 nucleus (see PI. IV, fig. 8). These vary somewhat in size but are on 

 an average three or four times the dimensions of the nuclei of the 

 syncytium. These are found also in the branching and anastomosing 

 columns which fringe out from the larger mass, forming large areas 

 at this end of the pancreas, as well as in the neighbouring zymogen ous 

 tissue (Pi. IV, fig. 8). The relations of these spherical cells to the other 

 cells of the pancreas are unknown to us. 



In the pancreas of the duck we find the same three kinds of 

 tissue existing side by side, viz. the zymogenous tubules, and the bathy- 

 chrome tissue and leptochrome islets. There are also small masses of 

 haemolymph or splenic tissue to be seen hei'e and there in the sections 



In the sparrow we have so far been able to detect only the 

 leptochrome islets. 



C. Reptiles. 



The islets of Langerhans in Reptiles have been described by 

 several observers, notably by Giannelli and Giacomini^), Diamare '^), 

 and Laguesse"). Diamare appears to have seen islets in Lacerta 

 corresponding in all respects wüth the leptochrome islets of higher 

 animals. Laguesse, on the contrary, who worked at the ophidians 

 appears to have seen only islets corresponding to the bathychrome tissue 

 of birds*), to which we have already made reference (see pp. 9 and 10). 

 In the viper (Vipera aspis) he describes the differentiation of the 

 primitive cavities into ducts and seci'eting tissue, but lays stress on 



') Coram, scient, della R. Accad. dei fisioscritici di Siena, 1896; Gianelli, Atti 

 della ß. Accad. dei Fisiocritici , ser. IV, vol. X, Siena 1898; Comm. fatta alla E. 

 Accad. dei Fisiocritici nell Adunanza del 14. nov. 1898 etc. 



2} Internat. Monatsschr. f. Anat. u. Physiol. Bd. XVI, Heft 7/8, 1899, tav. I— III; 

 Anat. Anz. XV. Bd., 1899; Internat. Monatsschr. f. Anat. u. Physiol. Bd. XXII, 

 Heft 4/6, 1905, tav. 8, 9. 



') Loc. cit. 



■*) This is probably not the case (See Appendix). [Note added Jan. 1. 1907.] 



