No. I.] EYES OF ARTHROPODS. 223 



retinophorae. This tube, or style, for it is formed in exactly the 

 same way as the style in the compound eye, is continuous at its 

 inner end, with an axial nerve-fibre which passes through the 

 centre of the tube into the centre of the cone. It then divides 

 into several longitudinal branches, passing between the axial 

 faces of the rods. On the surface of the cone, in each angle, 

 are two longitudinal nerve-fibres. Each one of the rods 

 has very fine cross-striations, undoubtedly caused by the pres- 

 ence of extraordinarily fine nerve-fibrillae uniting the axial 

 nerves with the superficial ones, thus forming a system of cross- 

 nerve fibrillae, or a retinidium, similar to that described by me 

 in Pecten. 



Milwaukee, April ir. 



LITERATURE. 



(1.) DujARDiN, Fel. Annales d. Sc Natur., 3 Ser. Zool. Tom. 14, 

 1850. (Not accessible.) 



(2.) Leydig, Fr. " Vom Bau d. thierischen Korpers." Tubingen. 1864. 



(3.) Rabl-Ruckhard. " Studien iiber Insectengehirne." Arch. f. Anat. 

 u. Phys. 1875. 



(4.) DiETL, M. J. " Die Organisation des Arthropodengehirns." Zeit. 

 f. wiss. Zool. 27 Bd. 1876. 



(5.) Claus, C. " Zur Kenntniss d. Organisation u. d. feinern Baues der 

 Daphniden u. verwandter Cladoceren." Zeit. f. wiss. Zool. 27 Bd. 1876. 



(5.) Grenacher, H. " Untersuchungen uber das Arthropoden-Auge." 

 Auszug. Rostock. 1877. 



(7.) Berger, E. " Untersuchungen ii. d. Bau d. Gehirns u. d. Retina d. 

 Arthropoden." Arbeit, a. d. Zool. Inst. Wien. Tom. I. 1878. 



(8.) Flogel, J. H. L. " Ueber den einheitlichen Bau d. Gehirns in d. 

 verschiedenen Insecten-Ordnungen." Zeit. f. wiss. Zool. 30 Bd., Supl. 

 1878. 



(9.) LowNE, Thompson B. "On the Modifications of the Simple and 

 Compound Eyes of Insects." 1878. 



(10.) Claus, C. "Der Organismus d. Phronimiden." Arbeit a. d. 

 Zool. Inst. Wien. Tom. II., i. Hft. 1879. 



(11.) Grobeen, C. "Die Entwickelungsgeschichte d. Moina rectiros- 

 tris." Arbeit, a. d. Zool. Inst. Wien. Tom. II., 2. Hft. 1879. 



(12.) Newton, E. T. " On the Brain of the Cockroach." Quart. Journ. 

 Mic. Sc. No. 75. 1879. 



(13.) LowNE, Thompson B. " On the Compound Vision and the Mor- 

 phology of the Eye of Insects." Trans., Linnean Soc. of London. 1884. 



(14.) Viallanes, H. " I. Le Ganglion Optique d. 1. Langouste {^Pali- 

 nurus vulgaris')" An. d. Sc. Nat. T. 17. 1884. 



(15.) Viallanes, H. "II. Le Ganglion Optique d. 1. Lebellule {^sclma 

 maculatissima)" An. d. Sc. Nat. T. iS. 1S84. 



