1910.] 



O.V THE VARIETIES OF MUS RATTUS IN EGYPT. 



651 



Plate LIV. 

 The figui'es on this Plate are seini-diiii^ninnnatic. 



Acanthephj/ra dehilis A. M.-Edw. 



Fig. 1. A longitudinal section of a photophore from the protopodite of a pleopod. 

 The cellular layer (c), which is apparently derived from the epithelium, is 

 composed of long cells with densely staining nuclei at their outer ends. 

 The onlv cytoplasm which is visible lies between the nuclei and the inner 

 face of the'lens. X 210. (Compare fig. 1, PI. LI I.) 



Sergestes cliallengeri Hansen. 



Fig. 2. A longitudinal section of the ej'e-stalk showing the photophore {yli.) lying 

 close to the eye (e.) and separated from it by a curtain of black piginent 

 {■p.). X 160. 



3. A photophore from the penviltimate joint of the second maxillipede in trans- 



verse section. X 380. (Compare fig. 3, PI. LIU.) 



4. A transverse section of the branchial chamber showing an arthrobranch {a.) 



and one of the four photophores ( pA.) which are set in the roof of the 

 cavity and appear to illuminate the gills from above. X 44. 



5. The same photophore on a larger scale. The two layers of the lens (/./. and 



o.l.) and the first cellular layer (c.') are formed from the cuticuhir and 

 epithelial layers of the inner surface ot the branchiostegite. X 380. 



Reference letters : — 

 a. Arthrobranch. 

 h. Branchiostegite. 

 c. Cellular layer (in AcantJiep7ii/ra.) 

 (•'. First cellular layer (in Sergestes.) 

 c" . Second cellular layer {ywSergestes). 



c. Eye. 

 e.l. Epithelial cell-layer. 

 g. Cone of minute highl3' refractive 

 granules in close connection with 

 nerve-strand. 

 i.e. Inner cuticular layer of branchio- 

 stegite. 



i.l. Inner layer of lens. 

 m.l. Middle layer of lens. 

 n. Nerve. 

 o. Optic ganglia. 

 o.c. Outer cuticular layer of branchio- 

 stegite. 

 o.l. Outer layer of lens, 

 jp. Curtain of black pigment between 

 photophore and eye. 

 ph. Photophore. 



;•. Reflector or striated layer. 

 s.l. Sheathing layer of cells. 



2. On the Varieties of Mus rattus in Egypt ; with General 

 Notes on the Species having reference to Variation and 

 Heredity. By J. Lewis Bonhote, M.A., F.L.S., F.Z.S. 



[Received December 22, 1909.] 



(Text-figures 58-62.) 



While spending a few months recently at the Giza Zoological 

 Gardens, near Cairo, I was enabled through the kindness of the 

 Director, Capt. S. S. Flower, to examine a large number of the 

 common House Rats of the district. I gladly took advantage of 

 the opportunities thus offered, as I was convinced that a close 

 study of this species would throw some light both on the causes 

 of variation and on the inheritance of the varieties that are 

 found in such profusion in Mas rattus. 



In addition to the rats which were caught in the Gardens, 

 Dr. Charles Todd, of the Public Health Department, kindly 

 allowed me to examine and measure all the rats tliat came into 

 his hands during the time that I was in Cairo. Tlie.se rats were 

 taken in various towns and villages in the Delta by special catcher.s 

 employeil by tlie Public Healtb Department, tlie result l)eing that 



