PLATE 1 



1 Section involving the pigment-cell and the two retinulae of the eye. M, 

 myoid or proximal portion of the retinula, which bears the nucleus; E, base of 

 the wedge-shaped region of the retinula cut obliquely; R, rhabdome, showing 

 striae; P.N, nucleus of pigment-cell; P, pigment granule; Ms, muscle of proboscis, 

 •which passes by the eye. The plane of section is indicated by line / in figure 

 3. X 1500. 



2 Section of eye, parallel to the partition of pigment-cell and to the wedge- 

 shaped region of the two retinulae. The left side of the drawing is ventral, the 

 right dorsal. R, rhabdome: E, wedge-shaped body (ellipsoid): P, pigment 

 granules. X 1500. 



3 Diagram of a meridional section of eye. P.C, pigment-cell with its nucleus : 

 R, rhabdome: E, wedge-shaped region (ellipsoid) of retinula: M, proximal. part 

 of visual cell (myoid) : 1, plane of section of figure 1; ^, plane of section of fig. 5. 



4 Diagram of retinula of: I, Prorhynchus applanata.- //, Polycystis goettei; 

 and: /// vertebrate. /// is based upon Arey's figures. Line A-A' connects 

 the rhabdomes; line B-B', the refractive bodies (ellipsoids) : line C-C, the nuclear 

 bearing regions (myoids) of the retinulae. 



5 Transverse section of a retinula involving the rhabdome, R: the wedge- 

 shaped body (ellipsoid), E: and a part of the pigment-cell. The plane of the 

 section is shown by broken line 2 in figure 3. X 1500. 



472 



