^Eyes of Molluscs and Arthropods. 643' 



which, being retidily soluble in alcohol, produce the vacuolated ap- 

 pearance described above; tliey would tend to make that part of the iris 

 opaque, thus facilitating its function of modifying the intensity of the 

 light. 



In Galathea^ as well as in Pagurus and Palaemon, I have succeeded 

 in isolating, by maceration, the style of the retinophorae, which 

 was continnous. at one end, with the four segments of the 

 calyx, and, attheother, with the four rows of plates coustitut- 

 ingthe pedicel. In the centre of the style, the four hyaline stalks of the 

 retinophorae are inseparably united to form, as mPenaeus, a tube, which 

 near the pedicel has again the tendency to divide into four Segments 

 (lig. 117, PI. 31). There can be no doubt that the calyx, style and 

 pedicel (or the Krystallkegelzellen and rhabdoms of Gren acher), are 

 continnous parts of the four retinophorae, a fact that is fatal to Gre- 

 nacher's theory that the Krystallkegelzellen (or what corresponds to 

 my calyx of the retinophorae) are homologous with the cells of the 

 vitreous body in Spiders and Myriapods. There are besides several 

 other insurmountable objections to this theory, rendering it no longer 

 tenable. The real homologues of the vitreous cells of Myriapods, Spiders 

 and Hexapod ocelli, are those of the corneal hypodermis, which 

 I have been able to detect in all the genera that I have examined, 

 and which without doubt must be considered to be universally present ! 



For example, I have found the corneal hypodermis present in 

 Musca^ Mcmtis, Branchipus, Penaeus^ Palaemon^ Pagurus smdGalat/iea. 



The number of the retinulae in Palaemon, Galafhea, and Pagurus 

 is seven. the same as in Penaeus, but the nucleated portions, instead of 

 being situated close to the inner end of the style, are extended outwards 

 as far as the neck of the calyx. The four outer pigment cells form a 

 dense black circle, just above the former, and are continued outwards 

 toward the cornea, as well as in the opposite direction, as slender pig- 

 mented rods , which in the latter case become reduced to the colorless 

 and hyaline bacilli, and are continued, as such, up to the basal mem- 

 brane. 



The calyx of Galathea is very favorable for the study of the nerve 

 fibrillae which there form the retinidium. For this purpose, I 

 have prepared the cells by the same method used to dissolve the cuti- 

 cular substance of the rods in Haliotis. It also gave very good results 

 here, but did not dissolve the crystalline cone. In such preparations, 

 one could follow the external, longitudinal nerve fibres surrounding the 

 style, as well as the central, axial fibres (PL 31, figs. 131 and 132) up 



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