330 



PHYLUM ARTHROPODA. 



bodies, an outer and inner. About the vitrellae 2 (or 4) 

 pigmented cells (cf. Fig. 233) are disposed. They are the 

 iris pigment cells (the distal retinular cells of Parker). The 

 vitrellae abut internally against a group of elongated cells 



: i 



FIG. 232. The compound crustacean eye. A two ommatidia of Palaemon squilla. The 

 pigment is removed from the right-hand ommatidium. C Isolated crystalline body of an 

 ommatidium, consisting of four elements. D Transverse section through a retinula about 

 the middle of its length. B Section through the stalked eye of Branchipus ; E two omma- 

 tidia of the same on a larger scale. 



bm basal membrane ; c cornea ; d corneal lens ; go optic ganglion ; h (in E) len- 

 tigen cells ; hy unmodified hypodermis ; k crystalline cone ; Tc t outer crystalline body ; 

 kz vitrellae ; m muscle ; nf nerve fibres ; no optic nerve ; p (in E) pigment in retinula cells, 

 (in A) pigmented hypodermis cells ; p, (in A) mesoblastic pigment strands beween the omma- 

 tidia ; re retinular cell?, deprived of pigment in D ; rg retinal ganglion ; rh rhabdom. 

 (From Lang's Textbook, A C and D after Grenacher ; B and E after Claus.) 



forming the retinula (re) which constitutes the innermost element 

 of the ommatidium. The retinular cells in varying number 

 (4 in Mysis, 5 in Branchipus, 7 in Palaemon) are arranged about 

 the optical axis of the ommatidium, and, like the vitrellar and 



