194 



F. S. SJOSTRAND AND L. G. ELFVIN 



qu'il y a imbrication des prolongements longes par 

 les vesicules. Ici, les prolongements n'ont pas ete 

 interesses sur toute leur longueur. 



Un autre fait apparaissant sur la fig. 2 merite 

 d'etre souligne : en certains points (region comprise 

 entre les deux fleches), des cellules visuelles voisines 

 peuvent contracter, au niveau des prolongements, des 

 rapports directs d'apposition, sans interposition de 

 Telement interstitiel. De tels rapports sont tres 

 comparables a ceux observes, en microscopic elec- 

 tronique, au niveau des synapses centrales. 



BiBLIOGRAPHIE 



1. Carasso, N., Compt. rend. acad. sci. 242, 2988 (1956). 



2. Detwiller, S. R., /. Comp. Neurol. 36, 125 (1923). 



3. DE RoBERTis, E., Acta Neurol. Latiuoamericana 1 (1955). 



4. — /. Biopliys. Biochein. Cytol. 2, 307 (1956). 



5. RocHON-DuviGNEAUD, A., Aiiii. OcuHst. p. 16, (1917). 



6. Sjostrand, F. S., /. Cellular Comp. Physiol. 42, 15 (1953). 



7. — ibid, 42, 45 (1953). 



8. — Z. wiss. Mikroskop. 62, 65 (1954). 



9. Walls, G. L., Amer. J. Neurol. 17, 892 (1934). 



Some Observations on the Structure of the Retinal Receptors of the Toaci 



Eye as Revealed by the Electron Microscope 



F. S. Sjostrand and L. G. Elfvin 



The Laboratory for Biological Ultrastriictiire Research of the Deportment of Anatomy, 



Karolinska Institutet, Stockholm 



In earlier electron microscopic studies the receptor 



cells of the retina have been studied in guinea pig and 



perch eyes (4, 5) and in albino rat and mouse eyes 



(1, 2). In this paper the preliminary results are 



reported from a study of the rods and cones of the 



toad {Bufo bufo) retina. 



The retinas from adult animals were fixed in a buffered, 

 isotonic 1 % osmium tetroxide solution (pH 7.4) at - 4 C. 

 Embedding in methacrylate and sectioning on a Sjo- 

 strand ultramicrotome. 



The receptors of the toad retina consist of rods, 

 and single as well as double cones. The present 

 analysis deals with the outer and inner segments. 



The rods. — The outer segment consists of a stack 

 of double membrane disks similar to those described 

 in the guinea pig and perch retina (3, 4). They 

 differ, however, from the latter as to dimensions 

 and the number of incisions extending from their 

 periphery towards the center. The stack of disks is 

 enclosed in a membrane representing the plasma 

 membrane. The dimensions of the double membrane 

 disks are: base diameter 5-6 //, total thickness 1 10 A. 

 The osmiophilic layers of the two constituent mem- 

 branes are about 40 A thick and the less osmiophilic 

 layer separating the osmiophilic layers is about 30 A 

 thick. The average spacing is 190 A. 



The inner segment contains the ellipsoid which 

 occupies most of its distal part. The ellipsoid consists 

 of densely packed mitochondria as in the perch 

 retinal receptors (7). A Golgi apparatus has been 

 observed just proximally to the ellipsoid. 



The outer and inner segments are connected 

 through a number of fibrillar structures which are 

 in contact with the plasma membrane of the outer 

 segment and penetrate into the inner segment late- 

 rally to the ellipsoid (fig. 1). 



The cones. — The outer segment of the single cone 

 cell consists of a stack of double membrane disks 

 similar to those of the rod outer segment. However, 

 these disks show no incisions. A cilia-like structure 

 similar to that described in the guinea pig retina (5) 

 seems to constitute the only direct connection be- 

 tween outer and inner segment. The outer segment 

 is bounded by a plasma membrane. A number of 

 cytoplasmic extensions from the inner segment sur- 

 round the basal part of the outer segment. 



Fig. 1. Part of an oblique to transverse section through a rod 

 outer segment. The fibrils, the surrounding membrane, 

 and the outer segment incisions are easily seen. Magnifica- 

 tion 23,000. 



Inset: Higher magnification of a fibril. Magnification 

 49,000. 



