

tsf.- 



186 PEOFESSOR E. RAY LANKESTER AND A. G. BOURKE. 



irregularity in the position of the phaosphere is very remarkable. 

 It is to some extent paralleled by Grenacher's observation of 

 the fact that in Epeira diadema all the nerve-end cells in 

 one eye (posterior dorsal) present a rod-like body in front of 

 the nucleus, whilst in a neighbouring eye (anterior dorsal) all 

 the nerve-end cells present a rod-like body posterior to the 

 nucleus. At the same time it is to be observed that the axial 

 rod of the Spider^s nerve-end cell must be considered as repre- 

 senting jiot only the phaosphere but also the laterally-placed 

 rhabdomere of the nerve-end cell of the Scorpion. 



The rhabdoms of the lateral eye of E. italicus are very 

 nearly as indefinite in their development as in the correspond- 

 ing eye of A. funestus. 



It will be seen below that in the central eye groups of five 

 nerve-end cells unite by means of their rhabdomeres to form 

 what Grenacher has called, in the multicorneal eye of Insects 

 and Crustaceans, a " retinula," and in the centre of this retiuula 

 is a five-ridged rhabdom Csee PI. XI, fig. 14). 



In the central eye of Scorpions this grouping or segregation 

 can be made out, though it is by no means so fully expressed 

 as in the multicorneal (polymeniscous) eye of Insects. In the 

 lateral eyes of the Scorpions, on the other hand, the grouping 

 into retinulae of the nerve-end cells and the formation of 

 rhabdoms from rhabdomeres is merely foreshadowed and not 

 completely carried out. 



In fig. 6 a portion of a section transverse to the long axis of 

 the nerve-end cells of the lateral eye of E. italicus is shown. 

 Rhabdomeres coloured yellow are seen in section, and it ap- 

 pears that they have a tendency to unite with one another, 

 though such a five-sided figure as that to be observed in the 

 corresponding region of the central eye (PI. XI, fig. 15) is not 

 yet attained. 



In fig. 5 the appearance of the ends of the nerve-end cells, as 

 seen when the cuticular lens is removed, is shown. A tendency 

 of the cells to group in fives can be traced. The pavement-like 

 appearance of the ends of the long nerve-end cells when thus 

 viewed has given rise to the erroneous statement on the part of 



