THE CONNECTIVE-TISSUE FRAMEWORK OF THE RETINA. 279 



glioina by Virchow,* to point out that one of their essential con- 

 stituents coincides with the spongy substance (neuroglia), and that it 

 may also proceed from the external granule layer.f 



We are indebted to H. Miiller for our knowledge of peculiar 

 smooth stellate and anastomosing cells forming a double layer 

 in the Perch and Ruff or Pope (Acerina cernua), which lie on the 

 inner side of the external granulated layer (intergranule layer), 

 and are not ganglion cells. They may be found in many other 

 animals, though, perhaps, not always so easily isolable, and 

 form, where they attain their greatest development, as in 

 Fishes, a special layer lying to the inner side of the external 

 molecular layer, to which I have given the name of the stratum 

 in tergranulosum fenestratum.$ The substance of the nucleated 

 laminaB anastomosing together by means of processes resembling 

 sheets of perforated iron, frequently possesses the structure of 

 striated plexiform (Plagiostomata), or fibrillar (Perca), connective 

 tissue, and is often directly continuous, as I have shown, with 

 that of the radial supporting tissue. In Perca fluviatilis I 

 find this foraminated intergranular layer to be composed of 

 three separate layers. The middle one includes the flat stellate 

 cells, which frequently anastomose, but the processes of which 

 may be as broad as the cells, so that the layer rather resembles 

 a plexus of broad nucleated fibres. These are covered on one 

 side by a plexus of delicate fibres resembling the branched and 

 interwoven elastic fibres, which form a single layer of wide- 

 meshed tissue. On the other surface is a thin lamina of appa- 

 rently finely granular substance of great delicacy, containing 

 scattered nuclei, and perforated by round holes. 



W. Krausel) has recently described the external granulated 

 layer of the retina in Man and Mammals as being composed of 



* Vorlesungen uber Geschwulste, Band ii. , p. 158. 



t See Iwanoff in Graf e's A rchiv, Band xv. , Heft ii. , p. 84. Iwanoff 

 clearly goes too far in maintaining that in no case can glioma develop 

 from the external granule layer ; for neuroglia that is to say, spongy 

 connective tissue is, as I showed as long ago as 1859 in my treatise, De 



structura penitiori, unquestionably present in this layer. 

 Zeitschrift fur wissenschaftliche Zoologie, Band viii., p. 17. 

 De EetituK structura penitiori, p. 13, fig. 5, /, fig. 6. 

 Die Membrana fenestrata der Retina, pp. 7 19. Leipzig, 1868. 



