536 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



The rhabdome is a complicated structure, narrow 

 and spindle-shaped (figs. 33 and 34 and Text-fig. 2), 

 which used to be described as consisting of four parts, a 

 fact which induced Grenadier to conclude that it was 

 secreted by alternate retinular cells. It is now known 

 that the quadripartite appearance and form is illusory, 

 and is due to the peculiar manner in which the retinular 

 cells form the structure. 



Stb.x.— 



,;.••,•. J : 



Stb.I. 



Text-fig. 2. 



Every two retinular cells (reckoning the seventh one 

 as double) take part in the secretion of one quarter of the 

 rhabdome. These quarters — which may be separated 

 and are known as rhabdomeres — are each made up of 

 transverse plates alternately supplied by the two 

 cells (fig. 34). Any one retinular cell would have a 

 toothed or cogged appearance if it were separated 

 with its own portion of the rhabdome. The 

 whole rhabdome therefore is built up of a series of 

 transverse half -plates and Text-fig. 2 would represent a 

 diagrammatic eccentric longitudinal section in which the 

 " stiftchen " of each lamella are shown alternately with 

 cut ends and from the side. The arrangement reminds 

 one of the dovetailing of the edges of a box. In 

 transverse section the rhabdome is almost square, and it 

 is surrounded by a distinct investing sheath (" Schluss- 

 leisten," Schneider). Each of the half plates bears a 



